Fix for Issue #313

When looping over facets, change call to measure_set according to new interface which takes an integral_type and subdomain_id instead of the measure.
Add test of par_loop with dS and ds measure
Merge pull request #314 from firedrakeproject/fix_parloop_facet_measure

* fix_parloop_facet_measure:
  Add test of par_loop with dS and ds measure
  Fix for Issue #313