Guarantee HashDict.equal?/1 returns proper value when comparing subsets

Conflicts:
	lib/elixir/test/elixir/hash_dict_test.exs

Author: José Valim

lib/elixir/lib/dict/behaviour.ex

@@ -63,6 +63,9 @@ defmodule Dict.Behaviour do
 
   """
   defmacro __using__(_) do
+    # Use this import to guarantee proper code expansion
+    import Kernel, except: [size: 1]
+
     quote do
       @behaviour Dict
 
@@ -120,7 +123,9 @@ defmodule Dict.Behaviour do
       end
 
       def equal?(dict1, dict2) do
+        # Use this import to avoid conflicts in the user code
         import Kernel, except: [size: 1]
+
         case size(dict1) == size(dict2) do
           false -> false
           true  ->

lib/elixir/test/elixir/hash_dict_test.exs

@@ -52,6 +52,14 @@ defmodule HashDictTest do
     assert inspect(filled_dict(8)) =~ "#HashDict<"
   end
 
+  test "comparison when subsets" do
+    d1 = HashDict.new(a: 0)
+    d2 = HashDict.new(a: 0, b: 1)
+
+    refute HashDict.equal?(d1, d2)
+    refute HashDict.equal?(d2, d1)
+  end
+
   defp smoke_test(range) do
     { dict, _ } = Enum.reduce range, { HashDict.new, 1 }, fn(x, { acc, i }) ->
       acc = HashDict.put(acc, x, x)