Fine tune seeder and p2p peer handling

core: check negative value transactions. Closes #1109

jsre: fixes for concurrent use, improved timer handling

common/compiler: compile solidity contracts with std library

eth/downloader: silence "Added N blocks from..." if N == 0

p2p: new dialer, peer management without locks 

Fork fix

Hash 38f5bbbffd74804820ffa4bab0cd540e9de229725afb98c1a7e57936f4a714bc
ignored.

eth, eth/downloader: surface downloaded block origin, drop on error

core/vm: Cleanups & SUB output fix. Closes #1096

eth: expand acronym in log message from TD

Some JSRE methods (PrettyPrint, ToVal) bypassed the event loop. All
calls to the JS VM are now wrapped. In order to make this somewhat more
foolproof, the otto VM is now a local variable inside the event loop.

This detects hanging connections sooner. We send a ping every 15s and
other implementation have similar limits.

The most visible change is event-based dialing, which should be an
improvement over the timer-based system that we have at the moment.
The dialer gets a chance to compute new tasks whenever peers change or
dials complete. This is better than checking peers on a timer because
dials happen faster. The dialer can now make more precise decisions
about whom to dial based on the peer set and we can test those
decisions without actually opening any sockets.

Peer management is easier to test because the tests can inject
connections at checkpoints (after enc handshake, after protocol
handshake).

Most of the handshake stuff is now part of the RLPx code. It could be
exported or move to its own package because it is no longer entangled
with Server logic.

The previous limit was 10MB which is unacceptable for all kinds
of reasons, the most important one being that we don't want to
allow the remote side to make us allocate 10MB at handshake time.

p2p/discover: evacuate self from node database during iterations

to total difficulty

core/vm, rpc: added disasm to `ext_` RPC

core: added RPC sign back in