rebase -i: proper prepare-commit-msg hook argument when squashing

One would expect that the prepare-commit-msg hook gets 'squash' as the
second argument when squashing commits with 'rebase -i'.  However,
that was not the case, as it got 'merge' instead.  This patch fixes
the problem.
Signed-off-by: NSZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-rebase--interactive.sh

@@ -304,23 +304,28 @@ do_next () {
 
 		mark_action_done
 		make_squash_message $sha1 > "$MSG"
+		failed=f
+		author_script=$(get_author_ident_from_commit HEAD)
+		output git reset --soft HEAD^
+		pick_one -n $sha1 || failed=t
 		case "$(peek_next_command)" in
 		squash|s)
 			EDIT_COMMIT=
 			USE_OUTPUT=output
+			MSG_OPT=-F
+			MSG_FILE="$MSG"
 			cp "$MSG" "$SQUASH_MSG"
 			;;
 		*)
 			EDIT_COMMIT=-e
 			USE_OUTPUT=
+			MSG_OPT=
+			MSG_FILE=
 			rm -f "$SQUASH_MSG" || exit
+			cp -v "$MSG" "$GIT_DIR"/SQUASH_MSG
+			rm -f "$GIT_DIR"/MERGE_MSG || exit
 			;;
 		esac
-
-		failed=f
-		author_script=$(get_author_ident_from_commit HEAD)
-		output git reset --soft HEAD^
-		pick_one -n $sha1 || failed=t
 		echo "$author_script" > "$DOTEST"/author-script
 		if test $failed = f
 		then
@@ -329,7 +334,7 @@ do_next () {
 			GIT_AUTHOR_NAME="$GIT_AUTHOR_NAME" \
 			GIT_AUTHOR_EMAIL="$GIT_AUTHOR_EMAIL" \
 			GIT_AUTHOR_DATE="$GIT_AUTHOR_DATE" \
-			$USE_OUTPUT git commit --no-verify -F "$MSG" $EDIT_COMMIT || failed=t
+			$USE_OUTPUT git commit --no-verify $MSG_OPT "$MSG_FILE" $EDIT_COMMIT || failed=t
 		fi
 		if test $failed = t
 		then