Rails 4 Beta support
Merge pull request #84 from neersighted/patch-1

Rails 4 Beta support
Switch .rbenv to .ruby-version and update
Update Gemfile.lock for Rails 4 support
Make explicit warnings when an asset is not found
Make missing asset digest an error
Raise requirejs compilation errors and exit from node with code 1

This provides better feedback when errors are encountered instead of
raising the more dubious "Cannot compute digest for missing asset".
Addresses #108 #93
Merge pull request #110 from negative/fix-missing-asset

Raise requirejs compilation errors and exit from node with code 1
Merge remote-tracking branch 'upstream/master'