[tex-eplain] eplain usepackage problems on Mac OS X and cygwin

[Karl Berry]

    If I remember correctly, the automatic conversion is only
    possible with MetaPost output files (.mps).  

There is no actual "conversion" in this case.  pdftex simply knows how
to read MetaPost files, as a (very) special case of .eps.  (Hans got the
pdftex guys to implement it.)  

    This will cause the epstopdf script to be called behind the scenes
    for each .eps file you include.

... which, as you say, requires that \write18 be enabled, either via
-shell-escape on the command line, or the equivalent in texmf.cnf, etc.
Personally, FWIW, I prefer to convert images separately, usually in a
Makefile, since special options can be needed.

\convertMPtoPDF or other context features may not require \write18,
since tex is not being invoked directly.  I never looked into that.

karl