add unit test case for #2193(double billing)

bancor has wrong README

Error out when no .git directory exists

p2p memory leak fix

Fix nodeos tests to work on arch linux

Fix txn_test_gen's nonce generation (again)

Add check for no authority

Switch to billing each distinct account

added check to prevent sigabort in net_plugin #2324

P2p code cleanup

Simplify generating doxygen files

#2294 cleos - set reference block to LIB or user defined

feat(docker): add mongo_db_plugin support to docker

fix 2189 prioritize .wasm files over .wast files

Fix nonce usage in cleos & txn_test_gen

memory corruption fix: resize array to right size #2301

So bizarre how this works in same cases but not others.

Do it by the book -- this is an action on the system contract complete with an ABI

Fix for stale _head in fork_database 

Check git submodule status before building

allow popping back to null, this is the initial state of the fork database and if you have overly aggressive test cases that do bad things on the very first block of the chain, we can and should pop back to null

when a block is added to current tip of the chain and fails, clean up the stale _head pointer because in very rare and strange cases its used before the next valid block comes and corrects the mistake

GH #2198 Bring up to date with submodule HEAD.