Fix Page.copy() to copy child objects that are defined on a superclass of the model
Fix replace_text to catch child relations that are defined on a superclass
changelog entry for child_relations bugfixes
fix tests I broke by fiddling with the AdvertPlacement test model
add dj1.7 migration for adding 'colour' to AdvertPlacement test model
Merge pull request #599 from gasman/fix/child_relations

Fix page copy and replace_text to pick up child relations that are defined on a superclass