[NTG-context] 2DOWN imposition gives blank pages

[wwl at musensturm.de]

> The following produces a first page with p.1 on the right half, but
> a blank 2nd page:
> 
> \setuppapersize[A5,landscape][A4,landscape]
> \setuparranging[2DOWN,rotated]
> \starttext
> \input tufte
> \stoptext
> 
> That looks okay, except for the blank 2nd page.

This makes sense only with duplex printing. So the second blank page 
is ok.

> \setuppapersize[A5][A4,landscape]
> \setuparranging[2UP]
> \starttext
> \input tufte
> \page
> \input tufte
> \stoptext
> 
> produces a two-page document:
> 
> p.1: |   | 1 |  (i.e. blank left half, and original p.1 on the right
> half)
> p.2: | 2 |   |  (i.e. original p.2 on left half, blank right half)

This is ok, too. Print it in duplex (flip over short side) fold it 
and you will see.

> So in case I've confused the directions of 2UP and 2DOWN, I also
> tried:
> 
> \setuppapersize[A5][A4,landscape]
> \setuparranging[2DOWN]
> \starttext
> \input tufte
> \page
> \input tufte
> \stoptext
> 
> It produces:
> 
> p.1: |   |   |
> p.2: | 2 |   |

This makes no sense.

> \setuppapersize[A5][A4,landscape]
> \setuparranging[2UP]
> \starttext
> \null\page
> \input tufte
> \page
> \input tufte
> \stoptext
> 
> produces the following arrangement, which is close to what I
> expect:
> 
> p.1: |   | 1 |  (where the original p.1 is blank except for the page
> num)
> p.2: | 2 | 3 |

Ok, too. Print it.

Wolfgang