Modify notifyspent handler to take multiple outpoints.
Use btcd pver instead of wire pver in getinfo RPC.

The getinfo RPC should return the max protocol version btcd supports as
opposed to the maximum protocol version btcwire supports.  Currently they
are both the same value, so there is no issue.  However, they will not
always be the same.
Use btcd pver instead of wire pver in RPC encoding.

Along the same lines as the previous commit, the RPCs that return
serialized data structures should use the max protocol version btcd
supports as opposed to the maximum protocol version etcwire supports.
Improve getwork interaction with regtest mode.

Ordinarily, getwork will return an error if btcd is not connected to any
other peers.  This commit relaxes that requirement when running in
regression test mode since it is useful for development purposes.

While here, also improve check which returns an error from getwork is not
current to exclude the check when the best chain height is zero since the
code never believes it is current when at height 0.