eth/downloader: fix dysfunctional ignore list hidden by generic set

eth, p2p, rpc/api: polish protocol info gathering

accounts/abi: ABI fixes & added types

Infinite loop in filters

crypto/secp256k1: add C compiler flags for pkgsrc

pkgsrc is a cross-platform package manager that also
supports OS X.

miner: synchronise start / stop

This PR fixes an issue where the remote worker was stopped twice and not
properly handled. This adds a synchronised running check to the start
and stop methods preventing closing of a channel more than once.

eth: added new testnet peers

cmd/geth, cmd/utils, eth: group CLI flags by purpose

Godeps: upgrade github.com/huin/goupnp

Changed field `input` to new `inputs`. Addad Hash and Address as input
types.

Added bytes[N] and N validation

Fix for xeth OOM issue

There are a bunch of changes required to make this work:

- in miner: allow unregistering agents, fix RemoteAgent.Stop
- in eth/filters: make FilterSystem.Stop not crash
- in rpc/comms: move listen loop to platform-independent code

Fixes #1930. I ran the shell loop there for a few minutes and didn't see
any changes in the memory profile.

Argument parsing can lead to panic in rpc channel

eth: don't block sync goroutines that short circuit

 check argument type before parsing params
 recover from panic in ipc channel

cmd/utils, crypto: add --lightkdf flag for lighter KDF

makefile: fix evm ld flags, pass them to xgo too

rpc api: eth_getNatSpec

eth, xeth: fix GasPriceOracle goroutine leak

XEth.gpo was being initialized as needed. WithState copies the XEth
struct including the gpo field. If gpo was nil at the time of the copy
and Call or Transact were invoked on it, an additional GPO listenLoop
would be spawned.

Move the lazy initialization to GasPriceOracle instead so the same GPO
instance is shared among all created XEths.

Fixes #1317
Might help with #1930

* xeth, rpc: implement eth_getNatSpec for tx confirmations
* rename silly docserver -> httpclient
* eth/backend: httpclient now accessible via eth.Ethereum init-d via config.DocRoot
* cmd: introduce separate CLI flag for DocRoot (defaults to homedir)
* common/path: delete unused assetpath func, separate HomeDir func

tests: update JSON files, add new wrappers