[NTG-context] 2DOWN imposition gives blank pages

[Sanjoy Mahajan]

> texexec --pdfarrange --paper=a5a4 --2up yourfile.pdf

I tried a few experiments with no luck.  Not sure if it's a context or
texexec problem, or my confusion.  I made the multi-page p5.pdf from

\setuppapersize[A4][A4]
\starttext
\dorecurse{50}{
\input tufte
}
\stoptext

Then I ran 'texexec --pdfarrange --paper=a5a4 p5.pdf' (the --2up
doesn't change the error below) and got this error:

! Missing number, treated as zero.
<to be read again> 
                   a
\@@ppoffset ->a
               5a4
\calculatepaperoffsets ...lue {\??pp #1\c!offset }
                                                  \divide \scratchdimen \arr...
<argument> ...!height }\calculatepaperoffsets {A4}
                                                  \xdef \papersize {A4}
\firstofoneargument #1->#1
                          
\next1 #1,->\docommando {#1}
                            \doprocesscommaitem 
...
l.3 \setuplayout
                

texexec is doing the arranging by making the following 'texexec.tex'
file and then, I think, running texexec on it:

\definepapersize
  [offset=a5a4]
\setuplayout
  [backspace=0cm,
    topspace=0cm,
       width=middle,
      height=middle,
    location=middle,
      header=0pt,
      footer=0pt]
\setuppagenumbering
  [alternative=doublesided]
\starttext
\insertpages
  [p5.pdf]
  [width=0cm]
\stoptext

The 'offset=a5a4' is upsetting Context; according to texshow-web on
the garden, the offset should be a dimension.  Also, I couldn't find
(using grep) the string 'a5a4' in the context sources.

-Sanjoy

`Never underestimate the evil of which men of power are capable.'
         --Bertrand Russell, _War Crimes in Vietnam_, chapter 1.