Patch to userExit in ShowBase.py

I’d like to address the problem described in the post “Exiting like a gentleman” with the following patch to /direct/showbase/ShowBase.py in Panda 1.7.2:

2565c2565
<     def userExit(self):
---
>     def userExit(self, force=False):
2570c2570,2572
<         self.finalizeExit()
---
>         taskMgr.stop()
>         if force:
>             self.finalizeExit()