issue #198 add test

tests/comptests/20_upvals.lua

@@ -0,0 +1,29 @@
+g = compiler.load([[
+local a: integer = 1
+function f()
+  return function()
+     return function()
+       a = a + 1
+       return a
+     end
+  end, a
+end
+]]
+)
+assert(g and type(g) == 'function')
+g()
+assert(f and type(f) == 'function')
+h, b = f()
+assert(h and type(h) == 'function')
+assert(b == 1)
+k = h()
+assert(k and type(k) == 'function')
+b = k()
+assert(b == 2)
+b = k()
+assert(b == 3)
+l = h()
+assert(l and type(l) == 'function')
+b = l()
+assert(b == 4)
+assert('integer' == math.type(b))