connection: add wl_connection_copy_fds function

this function pipes filedescriptors from one connection to another
(from input buffer to output buffer). Handy in dump tool.
tools: add wayland-dump

This tool creates a socket, which the client will connect on and
can do 'anything' with the data flowing between client and display.

It's easily extensible by filters (function that is called for each
data in the socket)

Signed-off-by: Marek Chalupa <mchqwerty@gmail.com>