When handling attr matching, simply compare the directory path where the
attribute file resides to the path being matched.  Skip over commonality
to allow us to compare the contents of the attribute file to the remainder
of the path.

This allows us to more easily compare the pattern directly to the path,
instead of trying to guess whether we want to compare the path's basename
or the full path based on whether the match was inside a containing
directory or not.

This also allows us to do fewer translations on the pattern (trying to
re-prefix it.)

When determining whether some file matches an attr pattern, do
not try to truncate the path to pass to fnmatch.  When there is
no containing directory for an item (eg, from a .gitignore in the
root) this will cause us to truncate our path, which means that
we cannot do meaningful comparisons on it and we may have false
positives when trying to determine whether a given file is actually
a file or a folder (as we have lost the path's base information.)

This mangling was to allow fnmatch to compare a directory on disk to
the name of a directory, but it is unnecessary as our fnmatch accepts
FNM_LEADING_DIR.

When ignoring a path "foo/", ensure that this is actually a directory,
and not simply a file named "foo".

When a .gitignore specifies some folder "foo/", ensure that a file
with the same name "foo" is not ignored.

Ensure that when examining a .gitignore in a subdirectory, we do not
erroneously apply the paths contained therein to the root of the
repository.  (Fixed in c02a0e46).

Centralizing all IO buffer size values

Stash apply

Allow the baseline to be specified as an index, so that users
need not write their index to a tree just to checkout with that
as the baseline.

Adjusting stream buffer size to 64KB

64K is optimal buffer size per https://technet.microsoft.com/en-us/library/cc938632.aspx

Android build doesn't need deps/regex

Ensure frameworks are mentioned in libgit2.pc

When building on Mac OS X, the `CoreFoundation` and `Security` frameworks where missing from `Libs.private` in the generated `libgit2.pc` file.

deps/regex was included in Android build because Android NDK 4 has
a packaging bug and doesn't have the regular expression functions defined
in its libc.so. The bug has been fixed in subsequent Android NDK releases.

If it is still necessary to work around the bug in Android NDK 4, we
should consider to use an option like ANDROID_NDK_RELEASE or
ANDROID_NDK_RELEASE_NUM.

Configuration changes for handling multiple of the same sections

Case insensitive checkout improvements

If a multivar exists within two sections (of the same name)
then they should both be updated in a `set_multivar`.  Ensure
that this is the case.