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