To many threads hung up

It was a long and painful exercise to develop the thread tree whereby many different strategies tried. Probably even all that's why I'll do a revert. Not at least due to all thread concepts were used. From AgsAsyncQueue to toplevel locking.

** (ags:26306): WARNING **: thread tree hung up

toplevel locking has one bad attitude. Namely hanging up the tree.

It seems never ending ...

The thread loop will be revised once again. Finally got to say, there too many commits dedicated to threads.