Vast P2P networking improvements, mainly for peer discovery, management
and handling.
Various crash fixes.
Merge branch 'develop' of github.com:ethereum/cpp-ethereum into develop

Conflicts:
	libethereum/State.cpp
Peer & key management.
Grow peers uses latest mechanisms.
More fixes.
Exception fix.
More network fixes.
Manage dead nodes.
Eth stores past peers and its own ID.
Throw exception for invalid instruction prior to determining gas.
Better drop off semantics.
Efforts to make reconnect timing strategy more expansive and consistent.
UX fixes to nodes view.
Pinging, stake disconnecting and better UI.
Remember last ping time.
Fix a previous bad fix.
Don't save peers with odd ports for now.
Kill old database (invalid transactions in there).
Avoid listening to peers telling us of wierd ports.