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: NJunio C Hamano <gitster@pobox.com>

t/t3101-ls-tree-dirname.sh

@@ -135,4 +135,10 @@ test_expect_success \
 EOF
      test_output'
 
+test_expect_success 'ls-tree filter is leading path match' '
+	git ls-tree $tree pa path3/a >current &&
+	>expected &&
+	test_output
+'
+
 test_done

tree.c

@@ -60,8 +60,12 @@ static int match_tree_entry(const char *base, int baselen, const char *path, uns
 			/* 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? */