Need one more round of testing for my branch

[David REVOY]

> What needs to be tested:
I switched to your branch and I will test more deeply than I can do this 
week-end during next week.
For the moment , I have this :

-  The brush strokes tend to experience a high slow down when doing a 
long stroke without releasing the stylus  ( ex: a 40 second stroke 
really get slow at the end ). Not sure if it was also the case in Master 
, not sure if this is a real issue as I usually not do so long stroke , 
but I saw it happen on shorter stroke with big brush. So , maybe 
revelent of a small problem.

- The display on the top of the canvas of many ruler assistant  ( 
without necesserely activate "assistant" in tool option ) make the brush 
system really slow. Not sure it was also the case in Master. ( 
perspective was always slow, I remember )

- For a side effect maybe,  "filters" not crash the same way than in 
master ( I know this are not expected in your test list )  ; like 
Curves/Levels/HSV etc. 'Preview' looks broken.

I will continue to note what I found.