Add make option to disable BerkeleyDB
Add make option to disable BerkeleyDB

Sample use:
BERKELEY_DB=0 make debug

This makes development with BlockchainLMDB easier when virtual methods
have changed and don't match BlockchainBDB.

ranok/bitmonero,eiabea/bitmonero,ranok/bitmonero,eiabea/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero