restrict specs to "expect" syntax
a helper to convert tests to specs

manual cleanup is still required
converted tests to specs

only syntactic changes, they are still semantically ugly; that will be
the next step
removed remains of test/unit

Conflicts:
	test/test_helper.rb
Revert "a helper to convert tests to specs"

This reverts commit ca1d8a8bbf98bf775d785249ceecf2b603604c30.
coverage: filter out specs and activesupport