Fix for broken request_uri on some systems (5.x)

This is a duplicate into the 5.x branch of an issue discovered in 4.7. For full details see

• the 4.7 version of the bug
• request_uri() broken under thttpd [IIS]
• the original forum topic

The attached patch addresses the issue by adding a comparision between $_SERVER['REQUEST_URI'] and $_SERVER['QUERY_STRING']. If QUERY_STRING contains a value and that value is not present in REQUEST_URI, an alternative method of determining request_uri()'s value is used.