[Tilesathome] threading renderer branch "burn cpu burn"

[Rene Wunderlich]

commit r12262
* add a workaround (the memory hole problem to minimize "gdlib?")
   restart after 10 jobs


i restart in threaded modus now the clinet after 10 jobs and hope this is ok for 
the most people

we have a memory problem "i think the gdlib" in forked modus have only the 
forked child the problem so it is not a problem from main process

in threaded modus have the main process a big tile from the work and leak ram.
at start use the client ~100mb with 8 childs "4 renderer 4 pngoptimize" and 
after a wile "100-800jobs >800mb..


i think this is the best/easyst way to protect the renderer and the system


René