Handle multiple target events before commit resume

Handle multiple target events before commit resume

Modify fetch_inferior_event to fetch (and handle) events from the target
as long as it provides events.

When resuming a thread that has hit a breakpoint (and it was decided
that it should be resumed), don't commit_resume just yet.  Wait until
the target has no more events to provide to do so.

Change-Id: Ia223a7d95dd5a4844c6a96e1125fb03d3e295584