The purpose of this feature is that the user knows whether
dependencies are satisfied. In particular, if they are not
he will be warned upfront, rather than finding out himself
in an abrupt way by trying to run something.

Prototype and Scriptaculous are no longer vendored, but provided by prototype-rails from now on, also the -j option of the application generator is removed

Some of the engines needs database. As engine needs to be run inside
Rails application, migrations and other database operations are run
from dummy application. To make that process simple I changed db
tasks to look for migrations in both engine's and application's
db/migrate directory. You can run all of the database tasks from
test/dummy or directly from engine with prefix app, like:

  rake app:db:migrate
  rake app:db:migrate:redo