Don't memoize in frozen objects. Closes #9

lib/carrierwave/mount.rb

@@ -232,6 +232,8 @@ module CarrierWave
     private
 
       def _mounter(column)
+        # We cannot memoize in frozen objects :(
+        return Mounter.new(self, column) if frozen?
         @_mounters ||= {}
         @_mounters[column] ||= Mounter.new(self, column)
       end

spec/orm/mongomapper_spec.rb

@@ -164,7 +164,7 @@ describe CarrierWave::MongoMapper do
       @doc = @class.new
     end
     
-    context "when file assigned" do
+    describe "when file assigned" do
     
       it "removes the file from the filesystem" do
         @doc.image = stub_file('test.jpeg')
@@ -178,7 +178,7 @@ describe CarrierWave::MongoMapper do
       
     end
     
-    context "when file is not assigned" do
+    describe "when file is not assigned" do
       
       it "deletes the instance of @class after save" do
         @doc.save