Offset uniqueness in vector of ColorSteps

[Regina Henschel]

Hi Armin,

you put the ColorSteps into a sorted vector with unique offsets of the 
ColorSteps.

I see a problem with "unique". Both OOXML and SVG allow several color 
stops to have the same offset. Users need it in OOXML and SVG gradients 
to create stepped gradients like those from ODF draw:gradient.

Thus forcing uniqueness in our core will give problems in import filter 
and in implementing the <svg:radialGradient> and <svg:linearGradient> 
from ODF.

Kind regards,
Regina