Split dependencies per platform.

Checked tests for ruby 1.9.3p194, 2.0.0p0, jruby 1.7.3 and rbx 2.0.0rc1. All are passing, there are only some warnings under ruby 2.0.0. 

Also added two missing tests for `:torquebox`. Nothing fancy, just somehow missed that version with `:torquebox` was not yet released and  wanted to check if everything is ok