Update db.cpp

Incorporate locks exhaustion fix per https://github.com/CryptoManiac/novacoin/commit/16e1262471dba899f3e9251b485abec219aec844
Update addrman.h

Resolve sqrt in addrman.cpp
Implemented getmininginfo report of network hash rate estimate, PoW reward.
Removed annoying "keypool return ..." debug message that isn't needed.
Average generate (local solo mining) hash rate over 30 seconds for more stable measurements.
Add checkpoint at block 75000.
Merge floodberry changes to YAC.
Clean up contrib files to reflect YACoin.
Add checkpoint at block height 90000.
Revert joebaurs RPC port change for now.
Add checkpoint at block 105000.
Add checkpoint at block 120K, tweak client version string, lots of YaCoin -> YACoin tweaking.
Added checkpoint at block height 135,000.
Added checkpoint at block height 150,000.
Added checkpoint at height 165,000.
Update README.md