[Omake] Rules execute in the wrong order

[Luis O'Shea]

> - an explicit ".SCANNER: scan-pdflatex-a.tex: x.pdf" dependency, or

Thanks.  I particularly like the above solution since it is so much
more restrictive (and, of course, one can encapsulate it into function
to make it easier to type).

In this particular case there is another solution: use
\usepackage{epstopdf} and then add -enable-write18 to PDFLATEXFLAGS.
Which I believe uncovers a small bug: PDFLATEXFLAGS is not actually
used in LaTeX.om.  For the moment I'll use the coarser LATEXFLAGS.