provide numeric stability on load/save

[Ulrich-windl]

When you save your SVG (for revision purposes) in some text-oriented revision control system, you may want to require that numeric constants remain the same for objects that were not changed.
I have an example where I had saved a drawing with "0.48.4 r9939" on a 32-bit Linux system featuring an AMD Phenom II CPU; after that I loaded the drawing with "0.48.5 r10040" on a 64-bit Linux system featuring an Intel Core I7 CPU. After changing some elements I saved the file and compared the changes. Then I found numeric changes in objects that were not touched!
Examples:
translate(0,-308.26769) changed to translate(0,-308.26766)
stroke-width:1.7716535 changed to stroke-width:1.77165353
translate(0,248.02462) changed to translate(-3.9999997e-7,248.02462)

In one case I found some text with a font size of something like 7.999*pt (which once definitely was 8pt; I cannot remember the digits where I put '*').

If one couldn't transform existing objects, I'd suggest to round after the n-th fractional digit, but in case you are (extremely) scaling the object, you might need the extra digits to prevent distortion.