Convert style name to symbol for the interpolator

Fixes #745

lib/paperclip/interpolations.rb

@@ -93,7 +93,7 @@ module Paperclip
     # If the style has a format defined, it will return the format instead
     # If the style has a format defined, it will return the format instead
     # of the actual extension.
     # of the actual extension.
     def extension attachment, style_name
     def extension attachment, style_name
-      ((style = attachment.styles[style_name]) && style[:format]) ||
+      ((style = attachment.styles[style_name.to_sym]) && style[:format]) ||
         File.extname(attachment.original_filename).gsub(/^\.+/, "")
         File.extname(attachment.original_filename).gsub(/^\.+/, "")
     end
     end
 
 

test/interpolations_test.rb

@@ -46,8 +46,11 @@ class InterpolationsTest < Test::Unit::TestCase
   should "return the extension of the file as the format if defined in the style" do
   should "return the extension of the file as the format if defined in the style" do
     attachment = mock
     attachment = mock
     attachment.expects(:original_filename).never
     attachment.expects(:original_filename).never
-    attachment.expects(:styles).returns({:style => {:format => "png"}})
-    assert_equal "png", Paperclip::Interpolations.extension(attachment, :style)
+    attachment.expects(:styles).twice.returns({:style => {:format => "png"}})
+
+    [:style, 'style'].each do |style|
+      assert_equal "png", Paperclip::Interpolations.extension(attachment, style)
+    end
   end
   end
 
 
   should "return the extension of the file based on the content type" do
   should "return the extension of the file based on the content type" do