QmlJS: Fix reference lookup cycles.

QmlJS: Fix reference lookup cycles.

Since several reference lookups involve Evaluate which may cause
further reference lookups, we need to be able to pass the existing
ReferenceContext to avoid cycles.

Change-Id: I2f1eeaad4d6b6ff094413d51077b03c985f6fab4
Reviewed-on: http://codereview.qt-project.org/4653
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@nokia.com>