When moving a container to a mark, also check whether the container is being moved to its own descendant and reject the request if this is the case.
When moving a container to a mark, also check whether the container is being moved to its own descendant and
reject the request if this is the case.

fixes #1957

Chr1stoph/i3,acrisci/i3,Airblader/i3-original,acrisci/i3,acrisci/i3,Airblader/i3-original,stapelberg/i3,Airblader/i3-original,cornerman/i3,Matmusia/i3,shdown/i3,Airblader/i3,avrelaun/i3,MForster/i3,Chr1stoph/i3,Airblader/i3,cornerman/i3,EvilPudding/i3,strake/i3,pronobis/i3,cornerman/i3,Airblader/i3,strake/i3,stapelberg/i3,avrelaun/i3,MForster/i3,stapelberg/i3,Airblader/i3-original,avrelaun/i3,strake/i3,shdown/i3,strake/i3,ccryx/i3,i3/i3,ccryx/i3,Chr1stoph/i3,avrelaun/i3,EvilPudding/i3,Matmusia/i3,pronobis/i3,ccryx/i3,i3/i3,Matmusia/i3,pronobis/i3,pronobis/i3,Airblader/i3-original,MForster/i3,acrisci/i3,i3/i3,i3/i3,stapelberg/i3,strake/i3,cornerman/i3,Matmusia/i3,ccryx/i3,MForster/i3,Chr1stoph/i3,EvilPudding/i3,EvilPudding/i3,acrisci/i3,Airblader/i3,shdown/i3,shdown/i3