Adding new "addrlocal" field to RPC getpeerinfo.
The existing CNode::addrLocal member is revealed to the user,
as an address string, similar to the existing "addr" field.
Instead of showing garbage or empty string,
it simply will not appear in the output if local address not known yet.
Merge pull request #2929 from Krellan/addrlocal

Additional field to RPC getpeerinfo output: addrlocal