This is a single-line change that allows non-standard transactions to get into the transaction memory pool (and, therefore, relayed and written into blocks) on -testnet.
Satoshi suggested this to me in an email a few weeks ago, and I agree it is a good idea-- we should encourage people to experiment on -testnet with new features, or they will figure out less efficient ways of wedging what they want to do into the existing standard transaction types.