fmt {:g} will sometimes put in scientific notation, e.g. 1.0e6 when we
pass some sizes of numbers. PDF doesn't accept scientific notation for
numbers, so make sure we convert those. Postscript seems to accept these
just fine so limit the fix to PDF.
I don't know that we were hitting these before, but my previous fix for
the background position caused some exponentially formatted numbers.
Mike Williams
5d92b9ba4b