cloning an Environment should make a deep copy of its construction variables

spec/rscons/environment_spec.rb

@@ -1,5 +1,16 @@
 module Rscons
   describe Environment do
+    describe '.clone' do
+      it 'should create unique copies of each construction variable' do
+        env = Environment.new
+        env["CPPPATH"] << "path1"
+        env2 = env.clone
+        env2["CPPPATH"] << "path2"
+        env["CPPPATH"].should == ["path1"]
+        env2["CPPPATH"].should == ["path1", "path2"]
+      end
+    end
+
     describe '.parse_makefile_deps' do
       it 'handles dependencies on one line' do
         File.should_receive(:read).with('makefile').and_return(<<EOS)