The app-test program gets run by atk_test_util.c, and gets sent a SIGTERM when the parent process wants it to terminate. This is fine, but if app-test terminates forcefully with the default handler for SIGTERM, then libgcc won't get a chance to write out its code coverage information.
So, we install a signal handler for SIGTERM, and the handler exits the main loop.
This increases test coverage from 33% to 57%, so yay!
Fixes #56 (closed)