This is a fix for issue 3794 where editing the columns in a datagrid would lead to page rendering problems when switching to a different page via the paginator.
The issue is the inclusion of the 'gridonly=1' parameter in the paginator URLs that result after editing the columns.  render_paginator() is updated to exclude the gridonly parameter when producing the new URL query string.
(Note: I'm a little out of my comfort zone here, but this seems to be a sufficient solution.)

Tested with internal dev server and confirmed that switching pages via the paginator no longer results in rendering issues.