bcb11f1 (mingw: mark t9100's test cases with appropriate prereqs, 2016-01-27)
replaced "/bin/sh" in exec.sh by the shell specified in SHELL_PATH, but
that breaks the subtest which checks for a specific checksum of a tree
containing.
Revert that change that was not explained in the commit message anyways
(exec.sh is never executed).
Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>