Optional Background Process for immediate Schedular

Hi,
I use a video conversion engine to encode videos and create thumbails. I also use backgrund process to avaoid blocking the interafec for large videos. The problem is, the background process also works on the thumbnail generation, but I had timing issues, I cannot rely that the thumbnial is background processed on my next call. Thats why i "hacked" the immediate scheduler and added the option "skip background process".

I added a patch againts current head.