Cleanup account op validation logic for easier reading
Merge branch 'develop' of github.com:BitShares/bitshares into develop
Update submodules
Fix margin call on expired position.

The while loop was supposed to iterate over all cover positions looking
for expired orders to force them to cover. This is not the most
effecient approach, but it will work.
Add hardfork warning
Move balance_record impl to its own file