Fix memory leak of MuxWrapper object.
Fix memory leak of MuxWrapper object.

(Note by apenwarr: I used Roger's original patch as the basis for this one,
but implemented it a different way.  All errors are thus my fault, but Roger
gets the credit for actually tracking down the circular reference that
caused the memory leak.)

v2e4lisp/sshuttle,ru-faraon/sshuttle,xtaran/sshuttle,bitmonk/sshuttle,GrimDerp/sshuttle,GrimDerp/sshuttle,ru-faraon/sshuttle,sshuttle/sshuttle,michaelcontento/sshuttle,mralexgray/sshuttle,cgundogan/sshuttle,guiquanz/sshuttle,CasparLi/sshuttle,luthfihm/sshuttle,GrimDerp/sshuttle,CasparLi/sshuttle,v2e4lisp/sshuttle,xtaran/sshuttle,apenwarr/sshuttle,zabracks/sshuttle,mheiges/sshuttle,fastly/sshuttle,zabracks/sshuttle,dushmis/sshuttle,vStone/sshuttle,mralexgray/sshuttle,brianmay/sshuttle,luthfihm/sshuttle,guiquanz/sshuttle,dushmis/sshuttle,sshuttle/sshuttle,loadlj/sshuttle,luthfihm/sshuttle,dxq-git/sshuttle,fastly/sshuttle,dxq-git/sshuttle,brianmay/sshuttle,CasparLi/sshuttle,shaunstanislaus/sshuttle,vStone/sshuttle,sekka1/sshuttle,mralexgray/sshuttle,ru-faraon/sshuttle,shaunstanislaus/sshuttle,vStone/sshuttle,shaunstanislaus/sshuttle,xtaran/sshuttle,zabracks/sshuttle,v2e4lisp/sshuttle,fastly/sshuttle,dxq-git/sshuttle,sekka1/sshuttle,dushmis/sshuttle,cgundogan/sshuttle,loadlj/sshuttle,sekka1/sshuttle,michaelcontento/sshuttle,apenwarr/sshuttle,cgundogan/sshuttle,michaelcontento/sshuttle,brianmay/sshuttle,mheiges/sshuttle,bitmonk/sshuttle,brianmay/sshuttle,loadlj/sshuttle,guiquanz/sshuttle,bitmonk/sshuttle,mheiges/sshuttle