Allowing testing with mocked server

[jhthorsen]

I wonder if using an environment variable is ok or if I should do Mojo::IRC->new(testing => 1);

[marcusramberg]

I would prefer an env variable instead of tainting the API.

[jhthorsen]

What does that mean (prefer env variable)? Do you accept the PR or do you want something to change?

[marcusramberg]

I accept it. I think the env is better than putting it in the constructor.

[jhthorsen]

\o/