Log Message:
Update dvtm to 0.6.
PR#45315 by Bug Hunting.

Changes include:

 - window content buffering upon resize, this actually improves
    usability quite a bit. Thanks to Niki Yoshiuchi for the initial
    patch

 - multiplexing mode, press MOD+a and your keystrokes will be sent
    to all non minimized windows. Could be handy if you have to do
    something interactive simultaneously on multiple servers.

 - a bug fix which should prevent leaking open file descriptors