test-lib.sh: set prerequisite SANITY by testing what we really need
What we wanted out of the SANITY precondition is that the filesystem
behaves sensibly with permission bits settings.
- You should not be able to remove a file in a read-only directory,
- You should not be able to tell if a file in a directory exists if
the directory lacks read or execute permission bits.
We used to cheat by approximating that condition with "is the /
writable?" test and/or "are we running as root?" test. Neither test
is sufficient or appropriate in environments like Cygwin.
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>