Arity of functions

[David Jones <drj@...>]

It would be nice for some debugging type tasks if it was possible,  
using either the C or Lua Debug API, to get the arity of a function,  
that is its Proto's numparams and is_vararg field.

In a fevered moment I did think that #f could be the arity of the  
function f.  Kind of appealingly hacky, but there's no obvious way to  
encode the varargness as well.

drj