Fix git_remote_connected

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.