Add a new test case for upvalues, and enhance upvalue handling so that

they pass.

src/test/res/upvalues2.lua

@@ -0,0 +1,42 @@
+-- The point of this test is that when an upvalue is created, it may
+-- need to be inserted in the middle of the list, rather than always
+-- appended at the end. Otherwise, it may not be found when it is
+-- needed by another closure.
+
+local function test()
+   local x = 3
+   local y = 5
+   local z = 7
+   
+   local function f()
+      print("y=", y)
+   end
+   
+   local function g()
+      print("z=", z)
+   end
+   
+   local function h()
+      print("x=", x)
+   end
+   
+   local function setter(x1, y1, z1)
+      x = x1
+      y = y1
+      z = z1
+   end
+   
+   return f, g, h, setter
+end
+
+local f, g, h, setter = test()
+
+h()
+f()
+g()
+
+setter("x", "y", "z")
+
+h()
+f()
+g()