Assert equality, not object identity of sets in sparsity constructor
Minor refactoring of matrix unit tests.
Import numpy as np in test_matrices unit test
Docstrings for test_matrices
Check consistency of Map tosets for par_loop Mat arguments
Docstrings for indirect loop unit tests
Import numpy as np in indirect loop unit test
Add unit tests for mismatching itersets and tosets when calling par_loop
Assert that maps used in par_loop arguments are initialized and test for it
Docstrings for direct loop unit tests
Import numpy as np in direct loop unit test
Add unit test asserting Mat args can only have modes WRITE, INC
Move Map <-> Dat/Mat consistency checks to Arg constructor
Merge pull request #208 from OP2/misc-unit-test-fixes

Some unit test fixes, mainly relating to `par_loop`:

* check equality of `Set`s in `Sparsity` constructor
* check consistency of `Map` tosets for `par_loop` `Mat` arguments
* assert and test that `Map`s used in `par_loop` arguments are
  initialized
* add unit tests for mismatching itersets and tosets when calling
  `par_loop`
* add missing docstrings for (in)direct loop unit tests
* assert Mat args can only have modes WRITE, INC
* move Map <-> Dat/Mat consistency checks to Arg constructor