Added HSProgress.setParentWindow()

When a parent window is set, the progress window will show
as a sheet for that window.
Added patch_threaded_job_performer()

The modernized progress workflow doesn't allow for the old
fix of using the special ThreadedJobPeformer from the cocoa
module.

Therefore, we now have patch_threaded_job_performer(). If your
app need to call functions from CocoaProxy inside a threaded
job, call this at startup to wrap _async_run() into an autorelease
pool.