Basic calculations in X, Y, W, H input boxes

[Abhijit]

It would be good if basic math is allowed in the W/H and X/Y input boxes.
E.g. to move an object by d mm, i can select the object, select the X input box and then just append "+d" to the existing X value.
It would be fantastic if it could support units as well, but I have no idea about implemenation feasibility.

[su_v (suv-lp)]

Please add information about OS/platform and Inkscape version to the bug description, thank you.

Note: the requested feature already exists in the current stable release (0.91):
http://wiki.inkscape.org/wiki/index.php/Release_notes/0.91#Simple_calculations_in_spinboxes

[su_v (suv-lp)]

The feature had been requested in the past several times already, and the implementation which is available in current stable Inkscape 0.91 was tracked in
* Bug #171282 “Calculator in input fields”
  https://bugs.launchpad.net/inkscape/+bug/171282

Proposing to link as duplicate to bug #171282.