Add test for -[ImmediateRef copy] and document.

NEWS

@@ -3,6 +3,8 @@
   * Added ARM64 support (64-bit) for iOS. It is not yet enabled by default,
     in order to do so, add the following line to your project's Rakefile:
     app.archs['iPhoneOS'] |= ['arm64']
+  * Fixed a bug when copying an `ImmediateRef', which isn't needed anyways,
+    because a tagged pointer can not be duplicated either.
   * [Vendor] Fixed a bug where Xcode 6 would cache precompiled headers in a
     hidden location and subsequent builds could fail after cleaning.
   * [Vendor] Fixed a bug where a failed build could cause subsequent builds to

test/test/spec/immediateref_spec.rb

@@ -31,7 +31,7 @@ describe "ImmediateRef" do
     ref.ruby_instance_method.should.eql ref
   end
 
-  it "is able to dispatch methods to itself", :unless => bits == 64 do
+  it "is able to dispatch methods to itself", :if => bits == 64 do
     class NSIndexPath
       def ruby_instance_method
         self.indexAtPosition(0)
@@ -40,4 +40,9 @@ describe "ImmediateRef" do
     ref = NSIndexPath.indexPathWithIndex(42)
     ref.ruby_instance_method.should == 42
   end
+
+  it "does not actually create a copy, but instead returns itself", :if => bits == 64 do
+    ref = NSIndexPath.indexPathWithIndex(42)
+    ref.object_id.should == ref.copy.object_id
+  end
 end