High-res profiling changes - nested profiling, recursive profiling and profiling...

High-res profiling changes - nested profiling, recursive profiling and profiling points

* change the timekeeping to use a fixed-size stack of times rather than
  directly referencing the time counter structs
* start/stop the previous level timers during profiling stop/start
  (someone could probably turned the UNACCOUNTED timer into the "level 0 timer"
  taking out the special cases..)
* Add in some more profiling points which'll surface in later commits.