Committed initial support in query result row. Proper support for this feature also requires to changes to the query parsers. With just this change the excerpt function in the query statement keeps unchanged (without a parameter), but the result row recognizes a parameter for the rep:excerpt() column.
E.g. after executing the query:
//element(*, nt:file)[jcr:contains(jcr:content, 'foo')]/rep:excerpt()
One can now get an excerpt from the jcr:content node even though the result nodes are of type nt:file:
Row row = ...
Value excerpt = row.getValue("rep:excerpt(jcr:content)");
Committed in revision 531167