Fluid sim would stop or crash with node editor.
Bug was a real bad one - the code for giving out WM jobs was messed up for long.
It was giving a running fluid job to the compositer even... tsk!
I will go over jobs code carefully next days to see if it all behaves. Now it
allows per owner multiple jobs, provided it has different job_type set.
Also fixed: preview renders (material) were deadslow once a while - caused
by icon render setting miniature tile render sizes. Now it's fast again,
but there are still 3 icon jobs running per UI change... need to check what.