Testnet difficulty calculation changes, to take effect Mar 15 2014
Allow mining of min-difficulty blocks if 20 minutes have gone by without mining a regular-difficulty block.
Normal rules apply every 2016 blocks, though, so there may be a very-slow-to-confirm block at the difficulty-adjustment blocks.
Update version to 0.3.52
Merge pull request #54 from khalahan/master-testnet

Testnet difficulty calculation changes, to take effect Mar 15 2014