Don't calculate fingerprint when fingerprint can not be stored.

lib/paperclip/attachment.rb

@@ -106,11 +106,12 @@ module Paperclip
       return nil if uploaded_file.nil?
 
       uploaded_filename ||= uploaded_file.original_filename
+      stores_fingerprint = @instance.respond_to?("#{name}_fingerprint".to_sym)
       @queued_for_write[:original]   = to_tempfile(uploaded_file)
       instance_write(:file_name,       uploaded_filename.strip)
       instance_write(:content_type,    uploaded_file.content_type.to_s.strip)
       instance_write(:file_size,       uploaded_file.size.to_i)
-      instance_write(:fingerprint,     generate_fingerprint(uploaded_file))
+      instance_write(:fingerprint,     stores_fingerprint ? generate_fingerprint(uploaded_file) : false)
       instance_write(:updated_at,      Time.now)
 
       @dirty = true
@@ -119,7 +120,7 @@ module Paperclip
 
       # Reset the file size if the original file was reprocessed.
       instance_write(:file_size,   @queued_for_write[:original].size.to_i)
-      instance_write(:fingerprint, generate_fingerprint(@queued_for_write[:original]))
+      instance_write(:fingerprint, generate_fingerprint(@queued_for_write[:original])) if stores_fingerprint
     ensure
       uploaded_file.close if close_uploaded_file
     end

test/attachment_test.rb

@@ -997,7 +997,14 @@ class AttachmentTest < Test::Unit::TestCase
         assert_equal now.to_i, @dummy.avatar.updated_at
       end
     end
-
+    
+    should "not calculate fingerprint without fingerprint column" do
+      assert_equal false, @dummy.respond_to?(:avatar_fingerprint)
+      @dummy.avatar = @file
+      @dummy.save
+      assert_nil @dummy.avatar.fingerprint
+    end
+    
     context "and avatar_content_type column" do
       setup do
         ActiveRecord::Base.connection.add_column :dummies, :avatar_content_type, :string