Do not use GUID on dir in git init --shared=all on FreeBSD

It does not allow changing the bit to a non-root user.
This fixes t1301-shared-repo.sh on the platform.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -283,7 +283,7 @@ int adjust_shared_perm(const char *path)
 			    ? (S_IXGRP|S_IXOTH)
 			    : 0));
 	if (S_ISDIR(mode))
-		mode |= S_ISGID;
+		mode |= FORCE_DIR_SET_GID;
 	if ((mode & st.st_mode) != mode && chmod(path, mode) < 0)
 		return -2;
 	return 0;