Reset extraNonce only every 15 seconds, just in case some miner is updating time himself and stuff
Reset extraNonce only when prevBlock changes, so miners can continue updating the time on their work until it's stale
Merge branch 'getwork_dedupe' into unique_coinbase
Merge commit 'aa4a9c5250f94c82a9e4077a1b56ba634a9841fa' into namecoin_merge_v0.8
Merge commit '02d87b3aa375810bcd63dcf72637e788a75fc7d4' into namecoin_merge_v0.8
Merge commit 'b760e254584a85db7195a4b1a67731a8cc12f9ed' into namecoin_merge_v0.8