Fix Env-Options in GherkinRunner; Allow CamelCase custom runner names

I fixed two issues i ran into while building a custom runner. Both tests failed before.
I wasn't sure where to put the MyTestRunner in cli_spec.rb - if you have a better suggestion pls comment.

(Context: i'm building a custom runner which launches one vncserver per process (= one browser per process instead of one window of the same browser) in order to work around problems with watir-webdriver which we could not fix otherwise. But the improvements are generally useful for all custom runners.)