Fix debug information about finalizers

The flag CIST_FIN does not mark a finalizer, but the function that was
running when the finalizer was called. (So, the function did not call
the finalizer, but it looks that way in the stack.)

testes/db.lua

@@ -887,7 +887,7 @@ do   -- testing debug info for finalizers
 
   -- create a piece of garbage with a finalizer
   setmetatable({}, {__gc = function ()
-    local t = debug.getinfo(2)   -- get callee information
+    local t = debug.getinfo(1)   -- get function information
     assert(t.namewhat == "metamethod")
     name = t.name
   end})

testes/gc.lua

@@ -371,7 +371,7 @@ if T then
 
   warn("@on"); warn("@store")
   collectgarbage()
-  assert(string.find(_WARN, "error in __gc metamethod"))
+  assert(string.find(_WARN, "error in __gc"))
   assert(string.match(_WARN, "@(.-)@") == "expected"); _WARN = false
   for i = 8, 10 do assert(s[i]) end