Convert specs to RSpec 3 syntax

Converting specs to the new RSpec 3 syntax.  This was largely
automated using Transpec.

* Replaced 'obj.should' based tests with 'expect(obj).to' (including
  appropriate changes to negative tests).

* Replaced 'it { should … }' with 'it { is_expected.to … }' (including
  appropriate changes to negative tests).

* Replaced equality operators ('==' with 'eq', '=~' with 'to match',
  etc.).

* Replaced boolean matchers ('be_true' and 'be_false' with 'be_truthy'
  and 'be_falsey', respectively).

* Replaced 'obj.stub' with 'allow(obj).to receive'.

* Replaced 'obj.should_receive' with 'expect(obj).to receive'.

* Replaced all uses of symbols in descriptions with strings
  (e.g. 'describe :a_method do', with 'describe "#a_method" do');
  this use of symbols was never correct, and RSpec 3 now prohibits it.