[metapost] another pensquare bug

[Taco Hoekwater]

Taco Hoekwater wrote:
> 
> Afaik, there never was an actual crash reported, just wrong output.
> Unfortunately, it is possible that the fix that removes this crash
> is itself the cause of the hanging of 1.003 on that other input file.

It was. I have just committed #460, that seems to take care of
all the following related problems:

* #3 (that was already fixed, in an original and alternate form)
* #7 (that was fixed by the alternate form of the #3 fix)
* the hanging pens.mp in 1.003 (caused by the alternate fix to #3)
* the crashing on the example from this thread (fixed as a side-
   effect of the #3 fixes)

Complicated stuff, and I am not sure this covers all cases. To be
honest, I just tried various potential solutions until I found one
that satisfied the four test files. So: if there is someone who
understands the logic of envelope creation and would like to have a
look, a second pair of eys would be great. Just reply and I will
explain where to look, exactly.

But if I get no offers to do that within a day  or so, this will
become metapost 1.003.

Best wishes,
Taco