Improve OpenMP support.

*More robust parsing of directives.
*Add support for OpenMP runtime library.
*Handle conflicts with c++ keyword private THXS to Mehdi Amini's report.
*Refactor OpenMP stuff into a new module.
*Improve testbed based on OpenMP Validation Testsuite.
*Distribute a Python binding of libgomp.
Fix a few OpenMP bugs.

* Allow to attach directives on Pass nodes.
* Make sure OMP directives are not lost/misplaced when held by the final
  statement of a block.
Fix sections for OpenMP support
Add sleep function from time module
Add OpenMP tests
Merge pull request #45 from pbrunet/openmp

Openmp