OP2/PyOP2 — pull request #325 by wence- (2014-03-10 11:23:04+00:00)
Title: Fix TypeError issue with extruded property for Subsets

Simplify extruded property (set a flag to False on Sets, True on
ExtrudedSets) and make Subsets inherit from ExtrudedSets. This latter
change fixes strange TypeError issues when iterating over Subsets.