Enable paranoid corruption checks in LevelDB >= 1.16
In -? output: -keypool, -gen, -genproclimit depend on ENABLE_WALLET
Merge pull request #4177

cd01a5e Enable paranoid corruption checks in LevelDB >= 1.16 (Pieter Wuille)
Merge pull request #4511

a7e1d50 In -? output: -keypool, -gen, -genproclimit depend on ENABLE_WALLET (Zak Wilcox)
replace ComputeMinWork with CheckMinWork
Remove redundant pblock->nNonce = 0
Move UpdateTime to pow
Move CBlockIndex::GetBlockWork() to pow::GetLengthIncrement(nBits)
Simplify and rename CheckWork to ProcessBlockFound
Encapsulate proof of work generation in pow
Encapsulate CBlockHeader fields for pow checks
Encapsulate CBlockHeader fields for pow updates