Python3 support

Hey guys,

I cleaned up @bakhtiary's PR a bit, and fixed the remaining python3 incompatibilities. Here's the output of `nosetests` on OSX, using the latest master branch of https://github.com/embotech/ecos-python.

```
$ python --version
Python 3.4.2 :: Continuum Analytics, Inc.
rmcgibbo@MacBook-Pro  ~ (3.4)
$ nosetests cvxpy
..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
----------------------------------------------------------------------
Ran 1298 tests in 13.151s

OK
```