Giving a clearer error message if programs cannot be started because the set shell cannot be found, closes #470.
Merge branch 'OC1.3-MC1.6.4' of github.com:MightyPirates/OpenComputers into OC1.3-MC1.7.10
Merge branch 'OC1.3-MC1.7.10' of github.com:MightyPirates/OpenComputers into master-MC1.7.10