hook grunt.fail.warn and grunt.fail.fatal aliases, grunt.warn and grunt.fatal
Merge pull request #2 from HBOCodeLabs/mgreen/hookaliases

Grunt has aliases for some APIs that are intercepted by grunt-timer. grunt.fail -> grunt.fail.fatal, and grunt.warn -> grunt.fail.warn. The grunt-shell plug-in is an example that uses grunt.warn. These other functions need to be hooked to report the final time total.