pathspec: rename free_pathspec() to clear_pathspec()

The function takes a pointer to a pathspec structure, and releases
the resources held by it, but does not free() the structure itself.
Such a function should be called "clear", not "free".

Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -322,7 +322,7 @@ static int path_exists(struct tree *tree, const char *path)
 	pathspec.recursive = 1;
 	ret = read_tree_recursive(tree, "", 0, 0, &pathspec,
 				  reject_entry, &pathspec);
-	free_pathspec(&pathspec);
+	clear_pathspec(&pathspec);
 	return ret != 0;
 }