db: introduce Recover(); allows recovering database with missing or corrupted manifest
db: introduce Recover(); allows recovering database with missing or corrupted manifest

btcsuite/goleveldb,zzl0/goleveldb,conseweb/goleveldb,rentongzhang/goleveldb,no2key/goleveldb,ngaut/goleveldb,hustbill/goleveldb,chai2010/goleveldb,FactomProject/goleveldb,syndtr/goleveldb,trigrass2/goleveldb