This ends up issuing the message "X, should be quoted" even when quoting it won't work. The case I found was:
````
> be puppet apply -e 'define private() { }' --parser current
Warning: Future reserved word: private, should be quoted. In <string>:1. See http://links.puppetlabs.com/reserved-words-4
   (at /Users/andy/work/puppet/lib/puppet/parser/lexer.rb:225:in `block in <class:Lexer>')
Notice: Compiled catalog for aparker.corp.puppetlabs.net in environment nothere in 0.02 seconds
Notice: Finished catalog run in 0.03 seconds
````

Since this is inside the lexer it can't easily change the message based on where in the grammar this is, so maybe a different message should be used here?