Fix file and line number reporting of QML/JS errors

* Replace QUrl with QString in V4 for the source location (we don't need URL parsing)
* Replace line number and file in QV4::Exception with the information we retrieve from
  the stack trace of the exception.

Fixes about five tst_qqmlecmascript tests that relied on correct file/line number information

Change-Id: I2a3daa72be6c5587fd965211ea8f6fb77142e7ee
Reviewed-by: Lars Knoll <lars.knoll@digia.com>