(bug 20310) Invalid value of edit_diff
This change makes EditFilterMerged handler replace all \r\n with \n.
Parser::preSaveTransform replaces \r\n with \n for all texts, so
there are no \r in the database. The hook EditFilterMerged is run
before the text is processed by Parser::preSaveTransform, so the
diff will be useless if the client sends content with \r\n as line