semi-smart quotes in verbatim text?

[cormullion@mac.com]

This is puzzling me. If i type this in a text editor:

\starttext
These are 'quotes'.
\starttyping
let a = 'quoted string'
\stoptyping
\stoptext

I'm using dumb quotes (hex 27). ConText renders this as this:

These are ’quotes’.
let a = ’quoted string’

ie the quotes have been educated - although only half-educated, since  
the opening one should be an opening one, if you see what I mean. But  
I really don't want characters in the verbatim (typing) section to  
change...because when you copy them from the PDF into an editor, the  
code listings don't work!

There must be some kind of switch somewhere that stops ConteXt  
changing them?

thanks for any help