Add handling of value-type lists to QDeclarativeExpression::evaluate()

QDeclarativeExpression::evaluate() converts all arrays to QList<QObject *>,
even if the items cannot be represented by a QObject *. In case of a
string-list, a QList of null-pointers is returned (which isn't very helpful).
This patch makes evaluate() convert arrays, which contain ONLY value-type
items, into a plain QVariantList.

Change-Id: Ib8452cf9dd0241f146955f5de35336f48b9007c1
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>