Added new peerlocal field to RPC getpeerinfo per-node output

This exposes CNode::addrLocal to the user, formatted as a string, just like the existing "addr" field.
I named it "peerlocal" instead of "addrlocal" to avoid breaking scripts that grep on the word "addr".
Interestingly, the addrLocal structure isn't filled in properly in all cases (I have seen IPv6 nodes connect to my bitcoind but addrLocal contains only my IPv4 address), but at least this gives it exposure to aid in fixing this deeper bug that lies elsewhere in bitcoind.