Ctrl-C does not abort when C extension is running under python

[manodeep]

Seems that if the C function is running in the main python thread, then it is cumbersome to capture Ctrl-C. Easiest work-around might be spawn two python threads and run the calculations in the background thread while the main thread continues to run. If a KeyBoardInterrupt (or some other exception) is raised, then the main thread can send a SIGINT to the C function.