Preserve dnat mapping when used with localnet.

[gijsh]

This allows using proxychains as a means of just changing the destination IP and port of network traffic similar to iptables DNAT without the need for root permissions.

Example usage:

localnet 127.0.0.0/8 dnat 1.1.1.1:1234 127.0.0.1:8123

This will redirect traffic to 1.1.1.1 on port 1234 to 127.0.0.1:8123.

[rofl0r]

would you mind adding a small paragraph to src/proxychains.conf so people reading about dnat and localnet can figure out this is possible ? otherwise this functionality will be available only to those who study the commit history.