Make the setter detection in Options more robust

lib/paperclip/options.rb

@@ -54,7 +54,7 @@ module Paperclip
     end
 
     def method_missing(method, *args, &blk)
-      if method.to_s[-1] == "="
+      if method.to_s[-1,1] == "="
         instance_variable_set("@#{method[0..-2]}", args[0])
       else
         instance_variable_get("@#{method}")

test/options_test.rb

@@ -8,6 +8,13 @@ class MockAttachment < Struct.new(:one, :two)
 end
 
 class OptionsTest < Test::Unit::TestCase
+  should "be able to set a value" do
+    @options = Paperclip::Options.new(nil, {})
+    assert_nil @options.path
+    @options.path = "this/is/a/path"
+    assert_equal "this/is/a/path", @options.path
+  end
+
   context "#styles with a plain hash" do
     setup do
       @attachment = MockAttachment.new(nil, nil)