Change "Current" as in GetCurrentThread, GetCurrentStackFrame, etc, to...

Change "Current" as in GetCurrentThread, GetCurrentStackFrame, etc, to "Selected" i.e. GetSelectedThread.  Selected makes more sense, since these are set by some user action (a selection).  I didn't change "CurrentProcess" since this is always controlled by the target, and a given target can only have one process, so it really can't be selected.

llvm-svn: 112221