Fix test failures on Fedora

There, /bin/ls and /usr/bin/ls are hardlinked. Python's realpath
returns the latter. Obvious fix is to only compare realpaths, never
realpath with what you think the path is.
Merge pull request #251 from vbraun/fixtests

Fix test failures on Fedora
Rename main() and fix import

Calling the function main in the module main is just asking for
trouble. The

    from ..cli import main as cli_main
    cli_main(args, env, logger)    # module not callable

is one such instance of trouble.
Delete the YAML C backend

This would require compilation of the _yaml extension module. Since we
aren't going to do that, the cyaml.py is just dead wood. Also, makes
nosetests --with-doctests fail.
fix doctest in jsonschema
Merge pull request #252 from vbraun/doctest

Doctest fixes
Make docs actually build
Removing Python 2.6 reference