raster clarification added to gOE

All --

>         e.) [Resolved] getObjectExtent for raster elements [8]
>                 -- add sentence to gOE (w/ CGM:1999 refs.)  [7]
>                 -- Action:  editor to add to current-editor draft

This is now implemented in the current editors draft:
http://www.w3.org/Graphics/WebCGM/drafts/current-editor-21/WebCGM21-DOM.html#getObjectExtent

-Lofton.