added rakefile check for ENV['ARRAY_CYCLES_DISABLE'] (this can now live ...

...in source)

Hey guys,

I have two live games using RM now -- one using the cycle detector with no problems and one that hangs without ARR_CYCLES_DISABLE=1 specified at rake time. As I'm doing updates for the two projects, it's starting to be a headache to remember which one I use it on and which one I disable it on. I poked through the source and it seems pretty trivial to just add it as a config variable in the Rakefile for the project.

Now it can live in source and give me piece of mind! 

I only implemented my actual use case, but it would be trivial to change it so that it actually replaces the setenv call with the value specified by the @environment_variables hash... let me know!