ppc: compatibility w/ new btcnet.Params (CoinbaseMaturisy, StakeMinAge, ModifierInterval)
GetProofOfWorkReward implementation
kernel.go: fix candidates sorting
Squashed commit of the following:

commit 86b84e6d9bde7f30734f798684d5ba02b070d28b
Author: mably <f.mably@gmail.com>
Date:   Thu Sep 18 10:31:37 2014 +0200

    vSortedByTimestamp with equal block time fix, sort by hash added

commit e01995edcd2fe078020daa2b96f203c57476f69d
Author: kac- <6b6163@gmail.com>
Date:   Wed Sep 17 21:50:08 2014 +0200

    kernel.go: added hash comparison to blockTimeHashSorter for candidates

commit 31ffbcd18bcafd0f3b0b7854327294d43027d538
Author: kac- <6b6163@gmail.com>
Date:   Wed Sep 17 20:03:48 2014 +0200

    make this test pass