[OS X TeX] figures in plain TeX

[juan tolosa]

I am baffled. Since I joined the Mac OS TeX community, I was given a method for processing pictures in plain TeX, which has been working seamlessly—until today. 
I had transitioned from TeXtures, which used the \special{…} command for inserting pictures, to a more transparent, and more universally accepted method.

In particular, I used
\input miniltx.tex
and next, something like
\RequirePackage{graphicx} 
and then I inserted pictures using, for example
\includegraphics[height=60mm]{RubiKo}

Today, to my surprise, I found the method is not working anymore.

As soon as the \input miniltx.tex is typeset, I get an error. The console displays:

This is pdfTeX, Version 3.14159265-2.6-1.40.17 (TeX Live 2016) (preloaded format=pdftex)
 \write18 enabled.
entering extended mode
(./PicturesInPlainTex.tex
(/usr/local/texlive/2016/texmf-dist/tex/plain/graphics-pln/miniltx.tex)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/local/texlive/2016/texmf-dist/tex/latex/graphics-def/pdftex.def
(/usr/local/texlive/2016/texmf-dist/tex/generic/oberdiek/infwarerr.sty)
(/usr/local/texlive/2016/texmf-dist/tex/generic/oberdiek/ltxcmds.sty)
/usr/local/texlive/2016/texmf-dist/tex/latex/graphics-def/pdftex.def:1569: Unde
fined control sequence.
l.1569      \@ifpackageloaded
                             {pst-pdf}%          hv 20160630
? 
Process aborted

Does anyone have an advice?
Thanks,
                Juan
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