fix setmetatable() to match C version

src/test/res/metatables.lua

@@ -1,5 +1,31 @@
+package.path = "?.lua;src/test/res/?.lua"
+require 'ids'
+
 -- The purpose of this test case is to demonstrate that
 -- basic metatable operations on non-table types work.
 -- i.e. that s.sub(s,...) could be used in place of string.sub(s,...)
 local s = "hello"
 print(s:sub(2,4))
+
+local t = {}
+function op(name,...)
+	a,b,c,d = pcall( setmetatable, t, ... )
+	print( name, id(t), id(getmetatable(t)), id(a), id(b), id(c), id(d) )
+end
+op('set{}  ',{})
+op('set-nil',nil)
+op('set{}  ',{})
+op('set')
+op('set{}  ',{})
+op('set{}  ',{})
+op('set{}{}',{},{})
+op('set-nil',nil)
+op('set{__}',{__metatable={}})
+op('set{}  ',{})
+op('set-nil',nil)
+t = {}
+op('set{}  ',{})
+op('set-nil',nil)
+op('set{__}',{__metatable='abc'})
+op('set{}  ',{})
+op('set-nil',nil)