* teximg: The prefix is configurable, and has changed to not include the
nonstandard mhchem by default. (willu)
* teximg: dvipng is used if available to render images. Its output is
antialiased and better than dvips. If not available, the old dvips+convert
chain will be used. (willu)
* Drop suggests on texlive-science, add suggests on dvipng.