Percent values no longe work on shapes.

Reproduced with Inkscape 0.91+devel rev >= 13938 on OS X 10.7.5

Reproduced on Crunchbang Waldorf, Inkscape trunk rev. 13994.
The missing circle and rectangle still exist, but are very small (50% is converted to 0.5 and 25% to 0.25...).

 OK, this bug reveals all kinds of nastiness.

1. We shouldn't be setting the 'viewBox' if it is not already set. Inkscape normally does not change existing elements unless an element is actually edited inside Inkscape.

2. Setting 'viewBox' triggers an unnecessary rewriting of all the child elements. There is no reason to do this.

3. During rewriting an element with an SVGLength, only the 'computed' value is rewritten (which in the case of percent, is the percent value as the actual "computed" value is determined at rendering time). This leaves the 'unit' and 'value' parts incorrect which causes the "computed" value to be misinterpreted.

4. Changing the code to write out the 'value' and 'unit' in addition to the 'computed' value works for rendering an element but in editing an element (dragging a node), again only the 'computed' value is written leading to incorrect 'unit' and 'value' parts.

Updates 14004 and 14009 fix ellipses and rectangles with % values, respectively.

One more nastiness: Moving one node causes set() to be called for all attributes but update() is not called. This leaves the computed values where the unit is % (or 'em'/'ex') incorrect which means that the nodes corresponding to the attribute values are placed on the screen in the wrong positions. Also, undoing an action does the same thing. I've added 'viewport' to SPItem so that the viewport is cached. This can then be used in set() to calculate the correct computed values. One could image eventually preservering the use of % values as attributes are edited as the 'viewport' information is now available.

Percentage values confirmed fixed in 0.92, so the bug could be closed Fix released with no milestone.

@Tav, could you please check the other items you reported, and, if there's something to be fixed, rename the report accordingly (or open a new report)?
Thanks!