I did not notice that all icons in math/ are shared and in a0895046 I have
overwritten some of them. I am restoring them in the proper subdir.
Two of them, namely font.svgz and frac.svgz, give warnings that should
be addressed. Anyway, I see that these icons use fonts. They are better
substitued with paths (a menu entry in inkscape) because if the fonts
are missing on a system, the icons look different and, in general, they
may look ugly.
