Fix memory corruption

The QString constructor taking a QStringDataRef doesn't refcount,
so we need to do it manually.

Change-Id: I076df18cfdb94ef796a42281b7bb1027798b609c
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Add a QV4::Script class

The class is a replacement for v8::Script. Start using it
in various places.

Change-Id: Ie5537639e44fa1ee23aea8605eae3c736819ef52
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Replace usage of v8::Script and qmlModeCompile with QV4::Script

Change-Id: I114a0b7faed39be313cde5617a0ce4a06dece7e2
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>