Added --remove-dist-egg option

[radarhere]

Resolves #4981

Adds a --remove-dist-egg flag to setup.py. It removes any created dist/*.egg file. This is also added to make release-test.

[hugovk]

To try and keep the monster setup.py a bit leaner, do you think rm dist/*.egg in make release-test would be enough?

Prefixing like -rm dist/*.egg tells make to ignore any errors (e.g. file not found): https://stackoverflow.com/a/2670143/724176

[radarhere]

My thinking was to avoid removing any other eggs that might also be in the 'dist' directory - but I realise that's not really a situation that's likely to occur.

Ok, see #4992