(bug 34521) Returning to the previous page after logging in loses any array-valued...

(bug 34521) Returning to the previous page after logging in loses any array-valued parameters in the query string. This happens because WebRequest::getValues() calls getVal() which strips arrays, even though the doc comment says that no transformation is applied. Changed getValues() to call getGPCVal() instead. The only difference is that arrays are no longer stripped, so the doc comment is no longer a lie