Added spinach command runner
Merge pull request #263 from jvanbaarsen/patch-1

Added spinach command runner
Fix CI

The method of activating the desired rails version was not working
correctly.
Test against Rails 4.1.0.rc1
Fix rails version selection

Previous code wasn't working correctly
Fix tests for rails 4.1
Abort when bin/spring is called and Spring is already defined

See #252. If you have a Spring 1.0 binstub, but Spring 1.1 on your
system, then the Spring 1.0 binstub will activate Spring 1.1, which will
then try to load your bin/rails, which will then load spring... and on
in on in a loop until you run out of memory. This prevents that and
prompts you to upgrade your binstubs.