Merge pull request EOSIO#1804 from EOSIO/merge-664-try-3

Third try at getting a clean commit pushed. EOSIO#1614

fix the case of a producer in isolation producing blocks then later r…

…ejoining a network. On superdawn brach, DO NOT MERGE WITH MASTER

Restored per-connection tracking of blocks requested on a particular …

…connection. This solves the issue with connection resets killing synchronization

DO NOT MERGE - This branch is a fork specifically to support the comm…

…unity testnet while the master is still under development.