* change MuMaildirWalkMsgCallback so it take a full stat buf* instead of just

the ctime; then do the checking for the file size (st_size) in mu-index

  also, update a unit test which was using an invalid MuMaildirWalkMsgCallback

src/tests/test-mu-maildir.c

@@ -163,7 +163,7 @@ dir_cb (const char *fullpath, gboolean enter, WalkData *data)
 
 
 static MuResult
-msg_cb (const char *fullpath, const char* mdir, gboolean enter,
+msg_cb (const char *fullpath, const char* mdir, struct stat *statinfo,
 	WalkData *data)
 {
 	++data->_file_count;