attr.c: respect core.ignorecase when matching attribute patterns

attr.c: respect core.ignorecase when matching attribute patterns

When core.ignorecase is true, the file globs configured in the
.gitattributes file should be matched case-insensitively against the paths
in the working directory.  Let's do so.

Plus, add some tests.

The last set of tests is performed only on a case-insensitive filesystem.
Those tests make sure that git handles the case where the .gitignore file
resides in a subdirectory and the user supplies a path that does not match
the case in the filesystem.  In that case^H^H^H^Hsituation, part of the
path supplied by the user is effectively interpreted case-insensitively,
and part of it is dependent on the setting of core.ignorecase.  git will
currently only match the portion of the path below the directory holding
the .gitignore file according to the setting of core.ignorecase.

This is also partly future-proofing.  Currently, git builds the attr stack
based on the path supplied by the user, so we don't have to do anything
special (like use strcmp_icase) to handle the parts of that path that don't
match the filesystem with respect to case.  If git instead built the attr
stack by scanning the repository, then the paths in the origin field would
not necessarily match the paths supplied by the user.  If someone makes a
change like that in the future, these tests will notice.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>