Fix parameter checking for subgraphs

Hello @nicks, 

Please review the following commits I made in branch 'kyle-simplify-tests'.

41fe0e9b84da2bc9854e8b0b0427e24d96201bdc (2013-07-12 16:37:11 -0700)
Don't parameter-check graph.subgraph

0c20c4e69717b71845a0ecb1c5e8e0ce907a10a6 (2013-07-12 16:32:29 -0700)
Simplify failure tests


R=@nicks