Handle TreatWarningsAsErrors a bit better

Hello @nicks, 

Please review the following commits I made in branch 'nick-warnings'.

2ff4b9cb2f384fb66d389164fe56ff456bfc3ca0 (2013-09-17 22:56:53 -0400)
Update the plovr jar

34e63f131772931f3dbf7e8daf0c7b76651c8d8d (2013-09-17 22:56:44 -0400)
Handle TreatWarningsAsErrors a bit better


R=@nicks