Changes the way of Integrations verification

In ruby 1.9.3 and 2.0.0 (tested in 1.9.3, 2.0.0, 2.1.1 and 2.1.2) if I
check for `const_defined?('Bla::Foo')` I got NameError. Testing with
`const_defined?('Bla') && Bla.const_defined?('Foo')` works.