\to broken in figure captions

[Sanjoy Mahajan <sanjoy@mrao.cam.ac.uk>]

In inline math, \to works fine (produces a right arrow), but in a figure
caption all hell breaks loose.

The culprit may be this redefinition of \to in enco-ini.tex:

  $ find texmf -name '*.tex' |xargs egrep -n '\\((e|g|)def|let)\\to\b'
  texmf/tex/context/base/core-pos.tex:642:  %\edef\to  {\POSprefix#1}%
  texmf/tex/context/base/enco-ini.tex:1565:  {\appendtoks\let\to\everylowercase
  texmf/tex/context/base/enco-ini.tex:1570:  {\appendtoks\let\to\everyuppercase

[context : ver: 2006.04.17 23:14]

This test file:

\starttext
\placefigure[abc]{ABC $n\to1$.}{} \input tufte
\stoptext

produces lots of errors beginning with

ERROR: Missing control sequence inserted.

--- TeX said ---
<inserted text> 
                \inaccessible 
<to be read again> 
                   1
\convertargument #1\to #2->\dodoglobal \edef #2
                                               {\detokenize {#1}}
<argument> ABC $n\to 1
                      $.
\docompletefloat ... \doglobal \convertargument #6
                                                  \to \asciititle \ifnofloat...
<argument> ...abc}{figure}{ABC $n\to 1$.}\nextbox 
                                                  \else \docompletefloat {fi...
...
l.2 \placefigure[abc]{ABC $n\to1$.}{}
                                      \input tufte