Control deep copy depth for 'save as new' in admin with inlines

[heka]

Proposal:

Add 'save_as' class attribute to all InlineModelAdmin. By default it should probably True.

ModelAdmin could then be modified as followed:

    def get_formsets_with_inlines(self, request, obj=None):
        """
        Yields formsets and the corresponding inlines.
        """
        if '_saveasnew' in request.POST:
            inline_instances = [inline_instance for inline_instance in self.get_inline_instances(request, obj)
                                if getattr(inline_instance, 'save_as', True)]
        else:
            inline_instances = self.get_inline_instances(request, obj)

        for inline in inline_instances:
            yield inline.get_formset(request, obj), inline

This change will allow you to control the save_as behavior per inline