git-commit: "read-tree -m HEAD" is not the right way to read-tree quickly

It still looks at the working tree and checks for locally
modified paths.  When are preparing a temporary index from HEAD,
we do not want any of that.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/git-commit.sh b/git-commit.sh
index cad16a5..fdaedc0 100755
--- a/git-commit.sh
+++ b/git-commit.sh
@@ -360,7 +360,7 @@
 		if test -z "$initial_commit"
 		then
 			cp "$THIS_INDEX" "$TMP_INDEX"
-			GIT_INDEX_FILE="$TMP_INDEX" git-read-tree -m HEAD
+			GIT_INDEX_FILE="$TMP_INDEX" git-read-tree -i -m HEAD
 		else
 			rm -f "$TMP_INDEX"
 		fi || exit