Client IP address for TCP server sockets

This patch implements a way for a Jim script to find out the client's IP address for a TCP server socket connection. It does this by adding an optional argument to `$socket accept` that specifies the name of the variable to store the client address in (similar to how `$socket recvfrom` already works for UDP). 

I sent the patch to the mailing list earlier (<http://sqlite.org:8080/pipermail/jim-devel/2014-July/001001.html>) but didn't seem to get a response, so I'm making this pull request just in case it was overlooked.