Add tests for filesystem challenges (case and unicode normalization)

Add tests for filesystem challenges (case and unicode normalization)

Git has difficulties on file systems that do not properly
distinguish case or modify filenames in unexpected ways.  The two
major examples are Windows and Mac OS X.  Both systems preserve
case of file names but do not distinguish between filenames that
differ only by case.  Simple operations such as "git mv" or
"git merge" can fail unexpectedly.  In addition, Mac OS X normalizes
unicode, which make git's life even harder.

This commit adds tests that currently fail but should pass if
file system as decribed above are fully supported.  The test need
to be run on Windows and Mac X as they already pass on Linux.

Mitch Tishmack is the original author of the tests for unicode
normalization.

[jc: fixed-up so that it will use test_expect_success to test
on sanely behaving filesystems.]

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>