Added a SBListener parameter to Launch and attach calls to avoid a race

condition that could occur when launching or attaching. What could happen is
you would launch/attach to a process, then you would need to tell a listener
to watch for process state changed events. In this case, if you waited too
long to listen for events, you could miss the initial stop event, requiring
clients to listen, then check the process state. 

llvm-svn: 124818