Debug information about extra arguments from __call

'debug.getinfo' can return number of extra arguments added to a call by
a chain of __call metavalues. That information is being used to improve
error messages about errors in these extra arguments.

testes/db.lua

@@ -624,6 +624,9 @@ local function f (x)
     end
 end
 
+assert(debug.getinfo(print, 't').istailcall == false)
+assert(debug.getinfo(print, 't').extraargs == 0)
+
 function g(x) return f(x) end
 
 function g1(x) g(x) end