[MERGE][bug #300177] Pass compression_parent as part of 'get_record_stream'

[Ian Clatworthy]

John Arbash Meinel wrote:
> The attached patch does 2 basic things:
> 
> 1) Changes the api so that the records (ContentFactory objects) from
> get_record_stream have a member called "compression_parents".
> 
> 2) Change insert_record_stream to use the compression_parents field, and
> take appropriate action.
> 
> 
> I went for the plural form, because it doesn't require a code change if
> we ever do multi-parent deltas.

I'm no expert at this level so I need a few questions answered before
I can vote tweak/approve.

bb:comment

> +                    # if c_parent is not None and c_parent != parents[0]:
> +                    #     raise AssertionError('Kndx files do not support'
> +                    #         ' non-left-hand compression parents.')

Did you mean to leave this commented out? Or implement that logic?

> +        # This indexs supports only a single compression parent, and it must be
> +        # one of the direct parents (for now)
> +        if len(compression_parents) > 1 or len(parents) < 1:
> +            return False
> +        # XXX: restore this to allow pack compression parents to be
> +        #       non-left-hand
> +        # if compression_parents[0] in parents:
> +        if compression_parents[0] == parents[0]:
> +            return True
> +        return False

Can you add some 'when' information to the XXX comment please?