Revert "Restore OpenMP support"

This reverts commit ba816dad7418693f497340b7b2caf3de3eddcf4a.
Add missing import for exceptions

This is not part of the validation and was broken during passes
splitting.
Merge pull request #256 from serge-sans-paille/remove-implicit-omp

Revert "Restore OpenMP support"
Merge pull request #257 from joker-eph/missing_import

Add missing import for exceptions
Re-enable testsuite for numpy
WIP - fix dangling ref