wildmatch test: perform all tests under all wildmatch() modes

wildmatch test: perform all tests under all wildmatch() modes

Rewrite the wildmatch() test suite so that each test now tests all
combinations of the wildmatch() WM_CASEFOLD and WM_PATHNAME flags.

Before this change some test inputs were not tested on
e.g. WM_PATHNAME. Now the function is stress tested on all possible
inputs, and for each input we declare what the result should be if the
mode is case-insensitive, or pathname matching, or case-sensitive or
not matching pathnames.

Also before this change, nothing was testing case-insensitive
non-pathname matching, so I've added that to test-wildmatch.c and made
use of it.

This yields a rather scary patch, but there are no functional changes
here, just more test coverage. Some now-redundant tests were deleted
as a result of this change, since they were now duplicating an earlier
test.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>