Use one script engine and one script debugger to avoid slow down of the skin parsing 

+ Using the debugger is much faster than before
+ The debugger is disabled on the spinny widget to avoid segfault (multithread?).
+ The global object is preserved from a skin context to it's children (as when there is one scriptEngine per context).
+ The translation js api is enabled (http://qt-project.org/doc/qt-4.8/qscriptengine.html#installTranslatorFunctions)
+ Removal of a circular reference of the global object in the svg extension 

I have a really fast SSD here so I didn't realize the slow down was so massive. Please tell me if there is another bottleneck on different setups.
Oh dear :). Can't say I remember that commit. All a blur really.

I took a look around and I don't think it's used (the line you pointed out is just a pointer assignment). It looks like we only pass by reference and use the copy constructor.