Lots of DistArray cleanup

1. Remove a couple of leftover C and Cython files (#38)
1. Improve our `test` target in our local Makefile.  Now one can just run `make test` at the top level to run all the tests, mpiexec-required or not.
1. Improve the test calls in the `.travis.yml` file
1. Clean up `distarray/core/error/`
    * One exception class (out of many) doesn't have the word "Error" at the end.  Fix this.
    * Also, for some reason it was reimplemented in the only module it's used in.  Remove that.
1. Remove `*` imports, except in `__init__.py`s.  Replace with explicit `from` imports. (#66)
1. Remove unused imports from many modules, identified by `pyflakes`.
1. Also, remove unused variables (and fix some bugs this uncovered) identified by `pyflakes`.
1. Capitalize error messages in `denselocalarray.py`
1. Strip all the trailing whitespace in the project with `autopep8`
1. Add simple "will it run" tests for wrappings of unary and binary numpy ufuncs, including their standard form, their form where the user provides an output array, and the form that is wrapped as a method attached to a `LocalArray`.
1. Shorten the code (discussed above) for wrapping unary and binary ufuncs.  This could also probably be done for the corresponding `LocalArray` methods (this is not done here).