Fix copying migrations from engines

There was a bug in ActiveRecord::Migration.copy method, which
prevented adding special comment about the origin of migration.

Because of that, the check if migration is identical or if it's
not and should be skipped was always saying that migration is
skipped, which was causing additional useless warnings about
skipped migrations.

activerecord/lib/active_record/migration.rb

@@ -461,11 +461,11 @@ def copy(destination, sources, options = {})
         source_migrations = ActiveRecord::Migrator.migrations(path)
 
         source_migrations.each do |migration|
-          source = File.read(migration.filename)
+          source = File.read(migration.filename).chomp
           source = "# This migration comes from #{name} (originally #{migration.version})\n#{source}"
 
           if duplicate = destination_migrations.detect { |m| m.name == migration.name }
-            options[:on_skip].call(name, migration) if File.read(duplicate.filename) != source && options[:on_skip]
+            options[:on_skip].call(name, migration) if File.read(duplicate.filename).chomp != source && options[:on_skip]
             next
           end
 
@@ -474,7 +474,7 @@ def copy(destination, sources, options = {})
           old_path, migration.filename = migration.filename, new_path
           last = migration
 
-          FileUtils.cp(old_path, migration.filename)
+          File.open(migration.filename, "w") { |f| f.write source }
           copied << migration
           options[:on_copy].call(name, migration, old_path) if options[:on_copy]
           destination_migrations << migration

activerecord/test/cases/migration_test.rb

@@ -2103,6 +2103,9 @@ def test_copying_migrations_without_timestamps
       assert File.exists?(@migrations_path + "/5_people_have_descriptions.rb")
       assert_equal [@migrations_path + "/4_people_have_hobbies.rb", @migrations_path + "/5_people_have_descriptions.rb"], copied.map(&:filename)
 
+      expected = "# This migration comes from bukkits (originally 1)"
+      assert_equal expected, IO.readlines(@migrations_path + "/4_people_have_hobbies.rb")[0].chomp
+
       files_count = Dir[@migrations_path + "/*.rb"].length
       copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy"})
       assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
@@ -2213,6 +2216,24 @@ def test_skipping_migrations
       clear
     end
 
+    def test_skip_is_not_called_if_migrations_are_identical
+      @migrations_path = MIGRATIONS_ROOT + "/valid_with_timestamps"
+      @existing_migrations = Dir[@migrations_path + "/*.rb"]
+
+      sources = ActiveSupport::OrderedHash.new
+      sources[:bukkits] = MIGRATIONS_ROOT + "/to_copy_with_timestamps"
+
+      skipped = []
+      on_skip = Proc.new { |name, migration| skipped << "#{name} #{migration.name}" }
+      copied = ActiveRecord::Migration.copy(@migrations_path, sources, :on_skip => on_skip)
+      ActiveRecord::Migration.copy(@migrations_path, sources, :on_skip => on_skip)
+
+      assert_equal 2, copied.length
+      assert_equal 0, skipped.length
+    ensure
+      clear
+    end
+
     def test_copying_migrations_to_non_existing_directory
       @migrations_path = MIGRATIONS_ROOT + "/non_existing"
       @existing_migrations = []