Reproject in multiprocessing

[fockez]

In my code, I have several images to reproject to a certain WCS. So I want to using multiprocessing pool to accelerate this procedure.
I pass the CCDData and target WCS to a function and it returns a new CCDData to main thread.
The problem is the program is always stuck at the last few images. When I commented out the reproject_interp all thing run good.