[Tilesathome] Tiles I render assinged to someone else

[Patrick Wilczek]

Hello,
due to the NoData-Problem and the forking issue, i set up 6 instances to 
keep my machine busy. If all instances are rendering, the tah website 
should show up an active request for each client (or more, if there is 
something in the upload queue). But sometimes (ca. 10%) a client is 
rendering and is not listed in active requests.  When I investigate 
whats going on there, the tile was indeed requested, but has been 
assigned to someone else. It is waste of resources to hand out the same 
tile twice for rendering.

Regards