The mptopdf script does standalone conversion from mpost to PDF, using
the supp-* and syst-* files. They also allow native MetaPost graphics
inclusion in LaTeX (via pdftex.def) and ConTeXt. They can be used
independently of the rest of ConTeXt, yet are maintained as part of it.
So in TeX Live we pull them out to this separate package for the benefit
of LaTeX users who do not install the rest of ConTeXt. This can be
found on CTAN in macros/pdftex/graphics.
