allVisible = function ( columnIndeces ) {
			for ( var k=0, kLen=columnIndeces.length ; k<kLen ; k++ )
			{
				if (  columns[columnIndeces[k]].bVisible === false ) { return false; }
			}
			return true;
		}
On each table draw, check the visibility checkboxes as needed. This allows any process to
update the table's column visibility and ColVis will still be accurate.
 @method  _fnDrawCallback
 @returns void
 @private