This commit does two things. One, it converts the return value of the QueueThreadPlanXXX

This commit does two things.  One, it converts the return value of the QueueThreadPlanXXX
plan providers from a "ThreadPlan *" to a "lldb::ThreadPlanSP".  That was needed to fix
a bug where the ThreadPlanStepInRange wasn't checking with its sub-plans to make sure they
succeed before trying to proceed further.  If the sub-plan failed and as a result didn't make
any progress, you could end up retrying the same failing algorithm in an infinite loop.

<rdar://problem/14043602>

llvm-svn: 186618