<rdar://problem/12446222>

Implement the ability for Python commands to be interrupted by pressing CTRL+C
Also add a new Mutex subclass that attempts to be helpful for debugging by logging actions performed on it

FYI of all interested - there is a separate deadlocking issue related to how LLDB dispatches CTRL+C that might cause LLDB to deadlock upon pressing CTRL+C while in a Python command.
This is not a regression, and was just previously masked by us not even trying to bail out of Python commands, so that it would not be clear from a user perspective whether we were
deadlocked or stuck in an inconsistent state within the Python interpreter.

llvm-svn: 170612