Improve image scaling. FOP 0.20.5 ignored scale=, but FOP 0.93 supports it. Switch the docbooks to 0.93 FOP. Add support to adjust PDF scale so it is expected size (not huge). Review and adjust all imagedata specs to work with 0.93 FOP (eliminate sizes in pixels, FOP using a different presumption about this). After this, it should be possible to specify no size or scaling and have things work, or to specify the size in some fixed dimension for PDF output (like inches) - it will be scaled for html output so it looks the same size, or to specify a scale= parameter.