do not modify options in image_tag

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -355,8 +355,8 @@ def font_path(source)
       #    <img src="/images/mouse.png" onmouseover="this.src='/images/mouse_over.png'" onmouseout="this.src='/images/mouse.png'" alt="Mouse" />
       #  image_tag("mouse.png", :mouseover => image_path("mouse_over.png")) # =>
       #    <img src="/images/mouse.png" onmouseover="this.src='/images/mouse_over.png'" onmouseout="this.src='/images/mouse.png'" alt="Mouse" />
-      def image_tag(source, options = {})
-        options.symbolize_keys!
+      def image_tag(source, options={})
+        options = options.dup.symbolize_keys!
 
         src = options[:src] = path_to_image(source)
 

actionpack/test/template/asset_tag_helper_test.rb

@@ -445,6 +445,12 @@ def test_image_tag
     ImageLinkToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
   end
 
+  def test_image_tag_does_not_modify_options
+    options = {:size => '16x10'}
+    image_tag('icon', options)
+    assert_equal({:size => '16x10'}, options)
+  end
+
   def test_favicon_link_tag
     FaviconLinkToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
   end