<rdar://problem/13883385>

Python breakpoint actions can return False to say that they don't want to stop at the breakpoint to which they are associated
Almost all of the work to support this notion of a breakpoint callback was in place, but two small moving parts were missing:
a) the SWIG wrapper was not checking the return value of the script
b) when passing a Python function by name, the call statement was dropping the return value of the function
This checkin addresses both concerns and makes this work
Care has been taken that you only keep running when an actual value of False has been returned, and that any other value (None included) means Stop!