Fix compilation warnings

Add git_note_foreach()

This reverts commit 1093e2de.

branch: cover with test that moving a non existing branch returns ENOTFOUND

branch: make git_branch_delete() return GIT_ENOTFOUND when the branch doesn't exist

See issue https://github.com/libgit2/libgit2/issues/680

Building a "shared object" (DLL) in Windows includes 2 steps:

- specify __declspec(dllexport)
  when building the library itself. MSVC will disallow itself from
  optimizing these symbols out and reference them in the PE's
  Exports-Table.
  Further, a static link library will be generated. This library
  contains the symbols which are exported via the declsepc above.
  The __declspec(dllexport) becomes part of the symbol-signature
  (like parameter types in C++ are 'mangled' into the symbol name,
  the export specifier is mingled with the name)

- specify __declspec(dllimport)
  when using the library. This again mingles the declspec into the
  name and declares the function / variable with external linkage.

cmake automatically adds -Dgit2_EXPORTS to the compiler arguments
when compiling the libgit2 project.
The 'git2' is the name specified via PROJECT() in CMakeLists.txt.

Add git_blob_create_fromdisk()

Fix build/runtime issues on Solaris

Attribute cache buster

Use -fvisibility=hidden in GCC builds

mergebase: enhance test code coverage

iterator: prevent git_iterator_free() from segfaulting when being passed a NULL iterator

Since we now rely on it (at least under Solaris), I figured we probably
want to make sure it's accurate. The new test makes sure that creating a
file with a name of length FILENAME_MAX+1 fails.

This function will create blobs in the object database from files anywhere on the filesystem. This can be run against bare and non-bare repositories.

On Solaris, struct dirent is defined differently than Linux. The field
containing the path name is of size 0, rather than NAME_MAX. So, we need to
use a properly sized buffer on Solaris to avoid a stack overflow.

Also fix some DIR* leaks on cleanup.

Improve repo initialization to be more like git

object: make git_object_lookup() return GIT_ENOTFOUND - The sequel

object: make git_object_lookup() return GIT_ENOTFOUND when searching for an existing object by specifying an incorrect type

This fix complements cb0ce16b and cover the following additional use cases

 - retrieving an object which has been previously searched, found and cached
 - retrieving an object through an non ambiguous abbreviated id

On Solaris, rmdir() throws EEXIST if the folder is not empty, so just add
one more case to check for that, alongside ENOTEMPTY.

This makes the git attributes and git ignores cache check
stat information before using the file contents from the
cache.  For cached files from the index, it checks the SHA
of the file instead.  This should reduce the need to ever
call `git_attr_cache_flush()` in most situations.

This commit also fixes the `git_status_should_ignore` API
to use the libgit2 standard parameter ordering.

Since Solaris does not support some of the same flags as glibc fnmatch(),
we just use the implementation we have for Windows.

Now that it's no longer a windows-specific thing, I moved it into compat/
instead of win32/

Use giterr_last() and make sure it's not NULL.

Fix MSVC compilation issue

    exp() is already defined in math.h. This leads to LMSVC complaining

    ..\..\libgit2\tests-clar\diff\blob.c(5): error C2365: 'exp' : redefinition; previous definition was 'function'

    Renaming the variable fixes this issue.