The right hand side of script string properties can be evaluated in entirely
dynamic scopes, due to QQmlExpressions' public API of allowing construction
from a QQmlScriptString and a variable scope/context. Nevertheless we should
compile these bindings at type compile time, as long as we make sure that the
compiled code doesn't try to do any compile time determined property lookups
and type resolution. This is implemented using a separate compilation pass
that ensures the disableAcceleratedLookups flag is set.

A few minor cleanups come with this patch:

 * Ensure that the property caches array is always symmetric to the list of
   compiled QML objects, as that allows the use of at() instead of value().
 * The code for creating a QML callable function object for a given run-time
   function is now centralized in a static function QmlBindingWrapper, used
   for script strings and bindings from custom parsers.

The provided unit test verifies the successful execution of the same script
string with two different scope objects.

Change-Id: Ica2cea46dd9e47263b4d494d922d3cc9664b08ae
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>