Random.new returns differently seeded objects

Specs of Random#bytes [0] suggest that instances of Random returned by
Random.new should be seeded differently. Specs of Random.new did not
specify this behaviour. This commits introduces an appropriate test.

[0] https://github.com/rubyspec/rubyspec/blob/c1ecc82/core/random/bytes_spec.rb#L37
Merge pull request #192 from jstepien/random-new-seeding

Random.new returns differently seeded objects