First commit to new extrusion branch. Previous functionality ported.
Fixed global attribute error when backend changes.
Extra flags added to OpenMP.

Conflicts:

	pyop2/openmp.py
OpenMP caching error and OpenMP args fixed.
IterationSpace gets a cache_key property using only extents and layers
Partition size fixed for general case.
Fixed unit test errors for sequential and OpenMP backends.
Fixed the OpenMP globals. OpenMP and sequential are compatible with trunk.
Extrusion test added.