Backported from X.org (libX11). Host.c has mainly been copied over from
 libX11, contaning 7db7451 as the top commit (which also contains the
 greatest change and silences the resp. compiler warning.

 commit 7db74514e454d3fc4ff70aa08ddac66bfffda4dd
 Author: Alan Coopersmith <alan.coopersmith@oracle.com>
 Date:   Tue Jul 23 22:18:46 2013 -0700

    Refactor common code from XAddHost & XRemoveHost into single function

    On the Xlib side, the only real difference is the mode flag we send
    to the server with the address, so just make that an argument to the
    function with the common code for packing the address into the request.

    (Aside from labels, gcc 4.7.2 generates identical code before & after
     this change due to inlining, verified via diff of gcc -S output.)
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>