Three minor changes in this patch:
- added UNLIKELY hint to few rarely executed branches;
- replaced couple of run time checks with debug assertions;
- moved check of presence of ittnotify tool from inside the function call.
These three changes incrementally improve library performance on SpecOMP2012 376.kdtree test to 1.5% in total
(used Intel 19 compiler + libomp on 2x24-core Intel CLX system).