Cleanup sim_t::main a bit.

git-svn-id: http://simulationcraft.googlecode.com/svn/trunk@17771 3b4652a1-8050-0410-ac47-3d40261b0f8b
Add functionality for thread priority. Implement it for the WinAPI.

git-svn-id: http://simulationcraft.googlecode.com/svn/trunk@17772 3b4652a1-8050-0410-ac47-3d40261b0f8b