Add a function dumping out a GBMI stack trace of the V4 engine.

Add an exported C-function dumping the JS stack trace which can be
invoked by a debugger with the address of an execution context
it finds in a complete stack trace.

Task-number: QTCREATORBUG-11144
Change-Id: I5314f6b24868f12d4f9dedd1c261658957e581ba
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Merge pull request #24 from xhaakon/mer-stable

Add a function dumping out a GBMI stack trace of the V4 engine.