path: add mpd_basename() function

This is like basename(3) but with predictable semantics independent
of C library or build options used.  This is also much more strict
and does not account for trailing slashes (mpd should never deal with
trailing slashes on internal functions).

src/path.c

@@ -290,3 +290,15 @@ void utf8_to_fs_playlist_path(char *path_max_tmp, const char *utf8path)
 	rpp2app_r(path_max_tmp, path_max_tmp);
 	strncat(path_max_tmp, "." PLAYLIST_FILE_SUFFIX, MPD_PATH_MAX - 1);
 }
+
+/* Only takes sanitized paths w/o trailing slashes */
+const char *mpd_basename(const char *path)
+{
+	const char *ret = strrchr(path, '/');
+
+	if (!ret)
+		return path;
+	++ret;
+	assert(*ret != '\0');
+	return ret;
+}