[renderd] Make renderd's TCP socket IPv6 compliant



git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29283 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4
[mod_tile] Enable mod_tile to connect to renderd via TCP socket

So far mod_tile could only connect to renderd via a unix domain socket.

Renderd was already able to accept tile rendering requests on tcp sockets
to enable it to be distributed accross multiple servers. With adding this
feature to mod_tile, it is now possible to have renderd on a different server
than mod_tile.

If multiple IPs are registered to the renderd dns entry, it supports a simple
form of automatic fail over, although a more sophisticated solution is likely
necessary for proper high availability setups.



git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29284 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4