OFFICE-3662 chart:interpolation

[Regina Henschel <regina.henschel@libreoffice.org>]

Hi all,

with OFFICE-3662 the attribute chart:interpolation (section 20.27, part 
3) has got the new values "step-center-x", "step-center-y", "step-start" 
and "step-end". They are correctly added in the text and in the schema.

Errors:
The generated text does not have the attribute values at all.
The change is missing in appendix G
The schema has no comment about the change.

Kind regards
Regina