Rounding issues when scaling using the toolbar and bounding box modes

[Giacomo Ciani]

Inkscape 0.48.5 r10040

When "geometric bounding box" is selected in preferences, scaling by inputting value in the toolbar is imprecise.

Steps to reproduce:
- in preferences, select "visual bounding box"
- set a document in pixel with a grid every 10 pixel
- create a 50 x 50 pixel square (using the grid snap)
- set the stroke width to 2 pixel.
- with the "select and transform" tool active, the width and height shown in the top toolbar are 52.000 px
- make sure the "affect stroke" button is deselected, and modify the width to 42.00. When you hit enter, the object is modified and the new value of 42.000 px is shown

Now:
- go into preferences, and change to "geometric bounding box"
- select the square (if it's not already). The toolbar reports a width of 40 px (it is not accouting for the stroke, as expected)
- modify that value back to 50. When you hit enter, the object is modified but the new reported value is not 50.000 px, but 50.256 px.
- only if you keep inputting 50.000 (4 times in this case) the value eventually converges ot the expected one.

Note that the first transformation using the visual bounding box is not necessary to reproduce the issue. It's just there to demonstrate the expected behavior.

[su_v (suv-lp)]

AFAICT this issue is already tracked in
- Bug #212768 “Geometric and Visual bounding box and object dimensions ”
  <https://bugs.launchpad.net/inkscape/+bug/212768>
(see also other duplicate report bug #398715, and other related reports mentioned in the comments of both reports).

Proposing to link as duplicate to bug #212768 - current stable 0.48 is known to be affected by it; the next major release 0.91 will include a fix.