basic framework for a leveldb blockchain. copied over bdb blockchain and renamed class prefixes to leveldb. methods need to be slowly migrated to using leveldb.
leveldb_blockchain initialisation and uninitialisation.
missing leveldb_blockchain file.
fetch and store block headers only.
purged out bdb txn_guard.
fetch block header by hash.
fetch_last_depth.
save_transaction and fetch_outputs.
fetch block depth
leveldb and bdb can work alongside each other now.
download blockchain from SOURCE to DEST. can resume from last place if stopped.
depth_comparator to order blocks by depth logically.
full leveldb backend working.
first step migration to new naming scheme for messages (now called primitives)
new names in bitcoin.hpp doc
remove ugly block variable name prefixes.
migration to new names for messages (now primitives).
naming migration complete.
Merge branch 'leveldb'
Merge branch 'rename'