SignTransaction creates a transaction but does submit it to the
network. SignTransaction returns a structure which includes the
transaction object details as well as the RLP encoded transaction that
could possibly be submitted by the SendRawTransaction method.
* 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
