Version 0.3.15

Version 0.3.15 is now available.

Changes:
- paytxfee switch is now per KB, so it adds the correct fee for large transactions
- sending avoids using coins with less than 6 confirmations if it can
- BitcoinMiner processes transactions in priority order based on age of dependencies
- make sure generation doesn't start before block 74000 downloaded
- bugfixes by Dean Gores
- testnet, keypoololdest and paytxfee added to getinfo