Move the handling of breakpoint conditions from the Private event loop to the StopInfoBreakpoint::DoActions, which happens as the 
event is removed.  Also use the return value of asynchronous breakpoint callbacks, they get checked before, and override the 
breakpoint conditions.

Added ProcessModInfo class, to unify "stop_id generation" and "memory modification generation", and use where needed.

llvm-svn: 137102