Add support for control signals (ex. Ctrl+C) in Windows

Hi everyone!

I am working on a cross-platform Tor controller/wrapper, and I encountered a minor inconvenience while writing code for stopping Tor in Windows.

Currently the only way to gracefully terminate Tor in Windows is to use the control port to issue the SIGINT signal, it would be beneficial for 3rd party programs which work with Tor to be able to invoke this procedure by using the native "control signals" provided to console programs in Windows.

I have made a patch which implements this functionality, I will post it soon, I am creating this ticket so that I can create a corresponding file in the changes directory :)

Thanks to nickm for some pointers about using the libevent event_active function to trigger the event, I decided to use the activate_signal function as it internally calls the suggested function and simplifies the code.

Trac:
Username: TheDcoder