Brought PayFile up to speed with Bitcoinj's introduction of InsufficientMoneyException.

Bitcoinj introduced InsufficientMoneyException, and PayFile was brought up to speed to include and use this where it could.

This requires a patch for Bitcoinj that has yet to be merged. 
https://github.com/bitcoinj/bitcoinj/pull/5. This fork can be downloaded here for testing: https://github.com/simondlr/bitcoinj/tree/insufficientmoney_patch.