Options: ensure copies do not share the underlying collection

Library/Homebrew/options.rb

@@ -54,6 +54,11 @@ class Options
     @options = Set.new(*args)
   end
 
+  def initialize_copy(other)
+    super
+    @options = @options.dup
+  end
+
   def each(*args, &block)
     @options.each(*args, &block)
   end

Library/Homebrew/test/test_options.rb

@@ -152,4 +152,10 @@ class OptionsTests < Test::Unit::TestCase
     debug = Option.new("-d")
     assert_equal [verbose, debug].sort, Options.coerce(array).to_a.sort
   end
+
+  def test_copies_do_not_share_underlying_collection
+    copy = @options.dup << Option.new("foo")
+    assert_empty @options
+    assert_equal 1, copy.count
+  end
 end