Implemented ActiveRecord::Migrations#copy based on James Adam's idea

ActiveRecord::Migration#copy allows to copy migrations from one place
to another, changing migrations versions and adding scope to filename.

For example:
ActiveRecord::Migration.copy("db/migrate",
        :blog_engine => "vendor/gems/blog/db/migrate")

will copy all migrations from vendor/gems/blog/db/migrate to db/migrate
with such format:

Versions of copied migrations will be reversioned to be appended after
migrations that already exists in db/migrate

1 files changed, 12 insertions, 0 deletions

diff --git a/activerecord/test/migrations/valid_with_timestamps/20100201010101_we_need_reminders.rb b/activerecord/test/migrations/valid_with_timestamps/20100201010101_we_need_reminders.rb
new file mode 100644
index 0000000000..d5e71ce8ef
--- /dev/null
+++ b/activerecord/test/migrations/valid_with_timestamps/20100201010101_we_need_reminders.rb
@@ -0,0 +1,12 @@
+class WeNeedReminders < ActiveRecord::Migration
+  def self.up
+    create_table("reminders") do |t|
+      t.column :content, :text
+      t.column :remind_at, :datetime
+    end
+  end
+
+  def self.down
+    drop_table "reminders"
+  end
+end
\ No newline at end of file