Hide single rake task

*sigh*

Ugh...

*shakes head*
Add deprecation warnings

Warn the users that these things are going to be removed in 1.0.
Rename test helper

Switch back to the default test helper name, for easier integration in Rails 4.
Update Rails 4 Gemfile

Use the beta1 gem now that it is released.
! Use newly added MiniTest::Spec::DSL

New direction for minitest-rails.
Instead of managing the ancestry to AS::TC, extend it with MT::S::DSL instead.
Allows for most of the complexity of minitest-rails to go away,
and we can focus on more on smoothing edges than maintaining hacks.
Thanks @zenspider!