p2p/nat: request timeouts for UPnP discovery

This includes a fix adding a timeout to router discovery requests.

tests: log coalescing fixes

cmd: transaction pool fixes and improvements 

eth/downloader: fix #1178, don't request blocks beyond the cache bounds

Removed the managed tx state from the chain manager to the transaction
pool where it's much easier to keep track of nonces (and manage them).
The transaction pool now also uses the queue and pending txs differently
where queued txs are now moved over to the pending queue (i.e. txs ready
for processing and propagation).

The transaction pool drops processed transactions on its own
during pool maintenance.

Add missing err checks on From()

core: re-add parallel nonce checks

core/vm: improve JUMPDEST analysis

eth/downloader: add a basic block download congestion control

Add EC signature validations before call to libsecp256k1

* JUMPDEST analysis is faster because less type conversions are performed.
* The map of JUMPDEST locations is now created lazily at the first JUMP.
* The result of the analysis is kept around for recursive invocations
  through CALL/CALLCODE.

Fixes #1147