JSDebugger: Break on Exception

The debugger breaks on Javascript exception. The error message is
printed on the ScriptConsole and the relevant code is marked with
a wavy underline.

Change-Id: I5e6f603430c3b8a0db450d1e8c821714ec0140ab
Reviewed-on: http://codereview.qt-project.org/4276


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>