49ebe51 fixed copying migrations, but existing migrations would still
trigger warnings. The proper way to compare migrations is to ignore
origin lines - if migration is identical it means that we can
silently skip it, regardless where it comes from.
The purpose of this change is to allow copying fail on the same names.
Migrations change database and they should be treated with caution,
if 2 migrations are named the same it's much better to skip migration
and allow user decide if it should be copied or not.
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
