Merge [pyunit] with [python-unittest]

The tags for pyunit (146 questions) and python-unittest (1,283 questions) should be merged, as both names refer to the same testing library.

Python's unittest documentation:

The Python unit testing framework, sometimes referred to as “PyUnit,” is a Python language version of JUnit, by Kent Beck and Erich Gamma.

Python 3 How to: Write Unit tests:

In the following blog post I’ll cover the following frameworks for unit testing.

1) PyUnit, also known as unittest in the Python modules.

I propose using python-unittest as the master tag, as it is the more commonly used tag.