Add debugging information to error message test (#5239)
Add debugging information to error message test (#5239)

One of the test cases in test/error_messages.coffee fails intermittently
in the Node.js ecosystem-testing tool CITGM. In an effort to help debug
what's going on when this occurs, this adds more information to the
AssertionError message in question.
shreeve/coffeescript,AndersonFirmino/coffeescript,jashkenas/coffeescript,cosmicexplorer/coffeescript,AndersonFirmino/coffeescript