Do not use mark() when marking ExecutionContexts

Some execution contexts in the parent chain can be allocated
on the C stack instead of the GC heap. Calling mark() on those would
push them onto the GC stack (which is identical to the JS stack).
In rare cases the reference can survive to live into the next call to
gc(), causing invalid accesses to already deleted contexts.

Change-Id: I709f58de27be9386cf70707c84e4c86c7c303fa7
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Fix crash when deleting component in Component.onComplete through loader

This is a regression introduced with Qt 5.3.0. The recursion watcher code that
is supposed to handle the test case of QTBUG-39775 can detect the recursion
into the object creator. However the boolean that indicates the recursion is a
member of a structure that's deleted afterwards. To avoid access to deleted
memory, this patch simply reference counts data structure shared between the
creators and also wraps the recursion watcher into a convenience class that
also increases/decreases the reference count accordingly.

Change-Id: I8d2e3e200ab1295e89d951e09f187d382a056d5a
Task-number: QTBUG-39775
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

Conflicts:
	src/qml/qml/qqmlobjectcreator.cpp
Fix memory leak in QQmlComponent::createObject

Regression introduced with 5.3.0. Prevent the leak of the object creator
on repeated createObject calls by using a scoped pointer.

Change-Id: Ib4fe7c9c6926c2390f7ae78f3287bb7da5f60527
Task-number: QTBUG-39742
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix QQmlComponent detailed description.

setParent() => setParentItem()

Task-number: QTBUG-39687
Change-Id: I67dc871a6d3b10af321d1f7b08921dcad0a6f19d
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Fix crash in QObjectWrapper

This can happen during QObject destruction, when
QObjectPrivate::deleteChildren() itself sets entries
in the children list to zero when deleting. These
zeros cause crash in markChildQObjectsRecursively().

Task-number: QTBUG-38635
Change-Id: I29ad9e793b78ca4e8d73fbb125f46db1b8292f20
Reviewed-by: Alan Alpert <aalpert@blackberry.com>