git-rebase--interactive.sh: Quote arguments to test

If /bin/sh is /bin/dash, then the script will display an error if
$parent_sha1 is undefined.  This patch works fixes the issue by
quoting both arguments to `test'.  Arguments composed solely of
variable expansions should always be quoted, unless we know for
certain that the contents are defined.

Signed-off-by: Michael W. Olson <mwolson@gnu.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-rebase--interactive.sh

@@ -110,7 +110,7 @@ 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 = $parent_sha1; then
+	if test "$no_ff$current_sha1" = "$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)