Powerstroke and other LPEs slow to respond with rev >= 15655

[Parcly Taxel]

(Trisquel 7.0, Inkscape r15660)

(1) Open the attached file, which contains a path with the powerstroke LPE
(2) Drag one of the stroke width control points

If rev >= 15655 then Inkscape will be slow in updating the path effect, and the lag is very noticeable. If rev < 15655 the dragging will proceed smoothly, no problem there.

The same lag occurs when dragging the control points for other LPEs, such as Perspective/Envelope and Envelope Deformation. I frequently use all three of the aforementioned LPEs, and as such the lag can get annoying at times.

[Jabiertxof (jabiertxof)]

Fixed in r.15637 of trunk

[Jabiertxof (jabiertxof)]

Also do some improvements to all point parameters like perspective, rotate copies, mirror symmetry, lattice2...