Make Python dependencies explicit

* Make python dependencies explicit, do away with the `{build:_with}` for bzip2, sqlite, openssl
* Update Python to 2.7.8, update IPython to 2.2

Can we please keep `{{build_with}}` in the `build` dependencies? Recently, I had to build `python` with `gdbm` and then I used:

      python:
        host: false
        build_with: |
          openssl, bzip2, sqlite, gdbm
        link: shared