rails/rails — pull request #17832 by claudiob (2014-11-29 02:24:54+00:00)
Title: Remove references to "debugger"

`byebug` has replaced `debugger` as the suggested gem to debug Rails code.
References to `debugger` were still in the code to support Ruby < 2.0.
Now that Rails requires Ruby >= 2.0, these references can be removed.