Fix checking for the presence of a flag

Enable mingw cross-compilation in travis-ci

Two things:
1) By default, Linux CMake puts -fPIC on the link line. So we remove that
for MINGW to avoid warnings that it will be ignored.
2) Similarly, move -fvisibility=hidden flag to be for non-mingw
compilation only to avoid warnings that it will be ignored.

Otherwise we can't cross-compile on Linux.

tests-clar/core: fix non-null warning

gcc 4.7.0 apparently doesn't see that we won't call setenv with NULL as
second argument.

The error codes from failed lookups of system and global files
on Windows were not consistent with the codes returned on other
platforms.  This makes the error detection patterns match and
adds a unit test for the various errors.

Fix bugs for status

This fixes two bugs:

* Issue #728 where git_status_file was not working for files
  that contain spaces.  This was caused by reusing the "fnmatch"
  parsing code from ignore and attribute files to interpret the
  "pathspec" that constrained the files to apply the status to.
  In that code, unescaped whitespace was considered terminal to
  the pattern, so a file with internal whitespace was excluded
  from the matched files.  The fix was to add a mode to that code
  that allows spaces and tabs inside patterns.  This mode only
  comes into play when parsing in-memory strings.

* The other issue was undetected, but it was in the recently
  added code to reload gitattributes / gitignores when they were
  changed on disk.  That code was not clearing out the old values
  from the cached file content before reparsing which meant that
  newly added patterns would be read in, but deleted patterns
  would not be removed.  The fix was to clear the vector of
  patterns in a cached file before reparsing the file.

windows: Properly expand all environment variables

Get user's home dir in UTF-16 clean manner

The function to convert UTF-16 to UTF-8 was only allocating a
buffer of wcslen(utf16str) bytes for the UTF-8 string, but that
is not sufficient if you have multibyte characters, and so when
those occured, the conversion was failing.  This updates the
conversion functions to use the Win APIs to calculate the correct
buffer lengths.

Also fixes a comparison in the unit tests that would fail if
you did not have a particular environment variable set.

We used to consider a missing core.bare option to mean that the
repository was corrupt. This is too strict. Consider it a non-bare
repository if it's not set.

On Windows, we are having problems with home directories
that have non-ascii characters in them.  This rewrites the
relevant code to fetch environment variables as UTF-16 and
then explicitly map then into UTF-8 for our internal usage.

Make git_futils_mkdir_r() able to cope with Windows network paths

Embedded makefile fixes

Build fixes for examples/

Add notice about release notes

Partially fix libgit2/libgit2sharp#153

By default, they are still not built, but hopefully, now that Travis is
building them, this will help stave off some of the bitrot.

git_reference_listall() -> git reference_list()

Cleanup

* indexer: remove leftover printf

* commit: remove unused macros COMMIT_BASIC_PARSE, COMMIT_FULL_PARSE
  and COMMIT_PRINT

Fix spelling errors.

Welcome to yet another libgit2 release, this one being the
biggest we've shipped so far. Highlights on this release
include diff, branches, notes and submodules support. The new
diff API is shiny and powerful. Check it out.

Apologies, one more time, to all the early adopters for the
breaking API changes. We've been iterating on the error
handling for the library until we reached its current state,
which we believe it's significantly more usable both for normal
users and for developers of bindings to other languages.
Also, we've renamed a few legacy calls to ensure that the whole
external API uses a consistent naming scheme.

As always, check the API docs for the full list of new API calls
and backwards-incompatible changes.

	http://libgit2.github.com/libgit2/

Changelog of new features follows:

Attributes:
	- Added function macros to check attribute values instead of having
	to manually compare them
	- Added support for choosing the attribute loading order (workdir files
	vs index) and to skip the systems' default `.gitattributes`
	- Fixed issues when fetching attribute data on bare repositories

Blob:
	- Added support for creating blobs from any file on disk (not
	restricted to the repository's working directory)
	- Aded support for smudge filters when writing blobs to the ODB
		- So far only CRLF normalization is available

Branches:
	- Added a high-level branch API:
		- git_branch_create
		- git_branch_delete
		- git_branch_list
		- git_branch_move

Commit:
	- Commit messages are now filtered to match Git rules (stripping
	comments and adding proper whitespacing rules)

Config:
	- Added support for setting and getting multivars
	- Added `git_config_get_mapped` to map the value of a config
	variable based on its defaults

Diff:
	- Added full diff API:
		- tree to tree
		- index to tree
		- workdir to index
		- workdir to tree
		- blob to blob

	- Added helper functions to print the diffs as valid patchfiles

Error handling:
	- New design for the error handling API, taking into consideration
	the requirements of dynamic languages

Indexer:
	- Added streaming packfile indexer

Merge:
	- Added support for finding the merge base between two commits

Notes:
	- Full git-notes support:
		- git_note_read
		- git_note_message/git_note_oid
		- git_note_create
		- git_note_remove
		- git_note_free
		- git_note_foreach

References:
	- Added `git_reference_name_to_oid` helper to resolve
	a reference to its final OID

	- Added `git_reference_cmp` to compare two references with
	a stable order

Remotes:
	- Added support for writing and saving remotes
		- `git_remote_add`
		- `git_remote_save`
		- Setters for all the attributes of a remote
	- Switched remote download to the new streaming packfile indexer
	- Fixed fetch on HTTP and Git under Windows
	- Added `git_remote_supported_url` helper to check if a protocol
	can be accessed by the library
	- Added `git_remote_list`

Repository:
	- Made `git_repository_open` smarter when finding the `.git` folder.
	- Added `git_repository_open_ext` with extra options when
	opening a repository

Revwalk:
	- Added support for pushing/hiding several references through a glob
	- Added helper to push/hide the current HEAD to the walker
	- Added helper to push/hide a single reference to the walker

Status:
	- Greatly improved Status implementation using the new `diff` code
	as a backend

Submodules:
	- Added a partial submodules API to get information about a
	submodule and list all the submodules in a repository
		- git_submodule_foreach
		- git_submodule_lookup

Tag:
	- Added `git_tag_peel` helper to peel a tag to its pointed object
	- Tag messages are now filtered to match Git rules (stripping comments
	and adding proper whitespacing rules)

Tree:
	- Killed the old `git_tree_diff` API, which is replaced by the
	new diff code.

Signed-off-by: Vicent Marti <tanoku@gmail.com>