Fuzz testing

For robustness, it would be good to have a separate test module that:
- is run with a random number of IPython engines (between 1 and 20 or so, inclusive)
- creates random distarrays with random sizes in each dimension (between 0 and 1e6, inclusive)
- with a random mix of undistributed, block distributed, and block cyclic distributed dimensions
- that tests ufuncs, reductions, and other fundamental stuff

We could test the edge cases in a separate test class as well -- size of zero in one or more dimensions, all dimensions undistributed, using a view with just one target /engine, etc.