match_tree_entry(): a pathspec only matches at directory boundaries

Previously the code did a simple prefix match, which means that a path in
a directory "frotz/" would have matched with pathspec "f".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/tree.c b/tree.c
index 03e782a..d82a047 100644
--- a/tree.c
+++ b/tree.c
@@ -60,8 +60,12 @@
 			/* If it doesn't match, move along... */
 			if (strncmp(base, match, matchlen))
 				continue;
-			/* The base is a subdirectory of a path which was specified. */
-			return 1;
+			/* pathspecs match only at the directory boundaries */
+			if (!matchlen ||
+			    base[matchlen] == '/' ||
+			    match[matchlen - 1] == '/')
+				return 1;
+			continue;
 		}
 
 		/* Does the base match? */