Do not fail on hierarchical tagnames.

This is a companion patch to 13d1cc3604a1a64cb5a6025bba8af8b74a373963
commit, which made hierarchical branch name possible.  "git tag
v0.99.9/a" would fail otherwise.

Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/git-tag.sh b/git-tag.sh
index bd92753..6130904 100755
--- a/git-tag.sh
+++ b/git-tag.sh
@@ -92,5 +92,6 @@
     object=$(git-mktag < "$GIT_DIR"/TAG_TMP)
 fi
 
-mkdir -p "$GIT_DIR/refs/tags"
+leading=`expr "refs/tags/$name" : '\(.*\)/'` &&
+mkdir -p "$GIT_DIR/$leading" &&
 echo $object > "$GIT_DIR/refs/tags/$name"