Adds a new API routine dr_track_where_am_i() which enables tracking of whereami for clean calls. This is off by default for performance reasons, which leads to clean calls being labeled initially DR_WHERE_FCACHE and then refined into DR_WHERE_UNKNOWN.
Adds a query routine dr_is_tracking_where_am_i() for use in the tracer where this tracking causes a short jump to not reach (#2147 (closed)).
Cleans up a hole in whereami tracking to include shared context switch code and do_syscall code along with other generated transition code as DR_WHERE_CONTEXT_SWITCH.
Adds labeling of DR_WHERE_SIGNAL_HANDLER for at least the ksynch_wait on a suspend signal; including other handler code is trickier and is left for future work.
Issue: #140