rebase -i: Make the condition for an "if" more transparent

Test $no_ff separately rather than testing it indirectly by gluing it
onto a comparison of two SHA1s.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-rebase--interactive.sh

@@ -164,7 +164,8 @@ pick_one () {
 	parent_sha1=$(git rev-parse --verify $sha1^) ||
 		die "Could not get the parent of $sha1"
 	current_sha1=$(git rev-parse --verify HEAD)
-	if test "$no_ff$current_sha1" = "$parent_sha1"; then
+	if test -z "$no_ff" -a "$current_sha1" = "$parent_sha1"
+	then
 		output git reset --hard $sha1
 		test "a$1" = a-n && output git reset --soft $current_sha1
 		sha1=$(git rev-parse --short $sha1)