commit: -F overrides -t

commit: -F overrides -t

Commit dbd0f5c7 (Files given on the command line are relative to $cwd,
2008-08-06) introduced parse_options_fix_filename() as a quick fix for
filename arguments used in the parse options API.

git-commit was still broken. This means

    git commit -F log -t temp

in a subdirectory would make git think the log message should be taken
from temp instead of log.

This is because parse_options_fix_filename() calls prefix_filename()
which uses a single static char buffer to do its work. Making two calls
with two char pointers causes the pointers to alias. To prevent
aliasing, we duplicate the string returned by
parse_options_fix_filename().

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>