Consensus rules dictate that objects can only be removed during the
finalisation of the transaction (i.e. after all calls have finished).
Thus calling a suicided contract twice from the same transaction:
A->B(S)->ret(A)->B(S) results in 2 suicides. Calling the suicided
object twice from two transactions: A->B(S), A->B, results in only one
suicide and a call to an empty object.

Our current debug tracing functionality replays all transaction that
were executed prior to the targetted transaction in order to provide
the user with an accurate trace.

As a side effect to calling StateDB.IntermediateRoot it also deletes any
suicides objects. Our tracing code never calls this function because it
isn't interested in the intermediate root. Becasue of this it caused a
bug in the tracing code where transactions that were send to priviously
deleted objects resulted in two suicides rather than one suicide and a
call to an empty object.

Fixes #2542

We used to have reporting of bad blocks, but it was disabled
before the Frontier release. We need it back because users
are usually unable to provide the full RLP data of a bad
block when it occurs.

A shortcoming of this particular implementation is that the
origin peer is not tracked for blocks received during eth/63
sync. No origin peer info is still better than no report at
all though.

Sign transaction returned the unsigned transaction rather than the
signed one.

Shutting down geth prints hundreds of annoying error messages in some
cases. The errors appear because the Stop method of eth.ProtocolManager,
miner.Miner and core.TxPool is asynchronous. Left over peer sessions
generate events which are processed after Stop even though the database
has already been closed.

The fix is to make Stop synchronous using sync.WaitGroup.

For eth.ProtocolManager, in order to make use of WaitGroup safe, we need
a way to stop new peer sessions from being added while waiting on the
WaitGroup. The eth protocol Run function now selects on a signaling
channel and adds to the WaitGroup only if ProtocolManager is not
shutting down.

For miner.worker and core.TxPool the number of goroutines is static,
WaitGroup can be used in the usual way without additional
synchronisation.

Fixes #2525

Context keys must have a unique type in order to prevent
any unintented clashes. The code used int(1) as key.

Fix it by implementing the pattern recommended by package context.

This fixes a few uses of unkeyed Body literals which go vet was
complaining about.