CScript::IsBlacklisted to check for known spam scripts

Initial list: SatoshiDice and BetCoin Dice
CTxMemPool::accept() : Drop blacklisted transactions
Blacklist "correct horse battery staple"
Merge commit '6ceca82' into spamfilter
Ignore transactions trying to spend coins received by blacklisted outputs
Revert old spam filtering

Reverts:
- 6521c7e71a974290a7a71f720bbdd75e3426146a Don't even accept transactions with blacklisted outputs into the memory pool
- 4977b7b2483e7355b7b7d8d44526b883a7192ef2 Blacklist 1JwS{S,T}* - correct horse battery staple spam
- 1fb2add4539577ced71233f8e3dfff4ec8474254 Merge branch block_dice into 0.8.0.eligius
Merge branch 'spamfilter' into 0.8.eligius
0.8.4.eligius3