feat($rootScope): allow $watchGroup to be passed an object

in case an object is passed instead of an array, the keys are the expressions to watch and the values are booleans indicating if this watched expression requires object equality check.
>we can have cases in $watchGroup that the updated value that never would have been reported to a watcher in $watch is passed only because some other expression in the group changed.

Can you explain this a bit further. I don't quite follow the sentence :-)