Ruby

[ruby/irb] Improve debug command tests
(https://github.com/ruby/irb/pull/594)

• Use require_relative for envutil.rb

Requiring test helper files with require_relative allows running the tests
with ruby -Itest test/irb/test_debug_cmd.rb without having to set up
the load path.

• Replace reline hack with TERM=dumb