#49 pixel measure for some primitives

[Bruce Sherwood]

It would be very helpful to be able to specify some things in terms of pixels, at least for the graphing machinery, where the scales are nonuniform.

In particular, if there were a dot or cylinder or sphere with pixel radius this could be used to plot dots (rather than the current nasty kludge of trying to plot little o's whose positioning is problematic cross-platform).

Or if it were possible to give a pixel radius to a curve, it would be possible to graph with thick lines, which is often highly desirable. And end-on curves with pixel radius could be used to plot dots.