swift234

[cmpcodesize] Prevent execution when importing

In order to prevent the Python interpreter from running code that is
meant to be executed directly, the convention is to check the context
in which the code is being interpreted.

Add a check for the context stored in the `__name__` variable, and only
execute the cmpcodesize script if it is being run as a command-line
script (that is, `__main__`).