Various changes towards making codebase compatible with 2.x and 3.x

[svisser]

This commit makes all non-risky changes towards making the codebase compatible with Python 2.x and Python 3.x. More work is needed to make all tests pass and to ensure Unicode / bytes separation happens properly.

The changes made in this commit are:

• Clean up DeprecationWarnings regarding outdated test method aliases.
• Changed various .iterkeys(), .itervalues() methods to be .keys() and .values() instead (which behave as expected in Python 3.x).
• Use new exception Exception as exc syntax instead of the outdated comma syntax for catching exceptions.
• Added three list() calls to ensure an assertion passes in def set_abilities in worker_handler.py. It may be possible to remove these list() calls and the assertion altogether but that should be done when going over the code for full Python 2.x and 3.x compatibility.

[svisser]

Closing this; please see https://pypi.python.org/pypi/py3gearman instead.