Backport of:

commit fc45fd6983e12c2701b445dae1f3d99988091eac
Author: Albert Astals Cid <albert.astals@canonical.com>
Date:   Thu Mar 20 16:28:15 2014 +0100

Don't crash on Runtime::getQmlImportedScripts

Task-number: QTBUG-37303

Change-Id: I083ca0cc3223fe0dbf1c768ad43a0d4927579867
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Backport of:

commit 354d3a17e2a772c467343a47f7b328ea8482f7fa
Author: Albert Astals Cid <albert.astals@canonical.com>
Date:   Thu Mar 13 17:09:39 2014 +0100

Clear the chain of incubated objects in QQmlIncubatorPrivate::clear

Change-Id: I432310c0e6006d567fd59b4b1021a9e1538ef78f
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Merge pull request #13 from mbrasser-jolla/crash-fixes

Backports of potentially useful fixes