Only replicate images between groups, or nodes, if the images are actually different or non-existent.

git-svn-id: https://svn.code.sf.net/p/freeghost/code/trunk@2517 71f96598-fa45-0410-b640-bcd6f8691b32
Merge svn with dev-branch
Merge master with svn
Merge master with dev-branch