t4135-*.sh: Skip the "backslash" tests on cygwin

The BSLASHPSPEC tests (11-13) fail on cygwin, since you can't
create files containing an backslash character in the name.
In order to skip these tests, we simply stop (incorrectly)
asserting the BSLASHPSPEC prerequisite in test-lib.sh.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -1061,7 +1061,6 @@ case $(uname -s) in
 	;;
 *CYGWIN*)
 	test_set_prereq POSIXPERM
-	test_set_prereq BSLASHPSPEC
 	test_set_prereq EXECKEEPSPID
 	test_set_prereq NOT_MINGW
 	test_set_prereq SED_STRIPS_CR