[GS] Update regression tests
Rename :w to UNKNOWN.hpp

Don't know what this file is supposed to be called, but :w breaks windows.
Merge branch 'develop' of https://github.com/BitShares/bitshares_toolkit into develop
Update fc submodule
Remove UNKNOWN.hpp

I think this is just an old version of engine.hpp. Drop it.
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Bugfixes in mail system
Remove testing mail server
don't try to build vm... just don't
Handle invalid signatures in mail
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Reorder destruction of objects owned by client (wallet, rpc_server, p2p, cli) to avoid executing RPC calls that would use the p2p node after the p2p node was destroyed.
Remove code that explicitly terminated owned threads, this is now done by fc::thread's destructor.
Revert "Revert "Prevent multiple RPC requests from executing at the same time.""

This reverts commit be479aea3036743a302168a465e868d9b14f5b51.
A little paving for mail-based transaction notifications
Implement transaction notification via mail
Merge branch 'develop' of github.com:BitShares/bitshares_toolkit into develop
Fix all cover interest calculation handling
Fix logic circa delegate pay changes
List mail servers if failed to send message
Mark manual cover transactions as market transactions
Rework mail server resolution

Now users publish mail servers as a list of account names. Each of these
account names will be looked up when sending mail, to get its published
IP endpoint for the RPC server.