suggesting change: lua_pcall error handlers to return multiple values

[Asko Kauppi <askok@...>]

In regards to the discussion concerning non-string error values, there  
is a certain detail of Lua that in my opinion would deserve a change.

The 'lua_pcall' function allows an error handler, which can grab the  
error message and modify it accordingly (normally, to add stack  
trace). This implies that the error "message" (as it is called in  
documentation) is a string. Non-string errors cannot be modified to  
have a stack trace.

Why not allow an error handler return multiple values?  What I have in  
mind is two (error value + stack trace string). Currently, 'lua_pcall'  
silently eats up any additional return values from the error handler.

-asko