rename test methods
reset BindingRepl.auto in setup and teardown methods.

the $auto variable is likely to be used when starting a script:
- $auto=ripl ruby hello/world.rb
- $auto=irb  ruby hello/universe.rb

in a scenario like that BindingRepl.auto would have a nil value.
at runtime the best way to change the auto order is through the
BindingRepl.auto= setter, but i have never actually wanted to
do that before.
remove freeze of DEFAULT_AUTO & LOOKUP
remove freeze of DEFAULT_AUTO and LOOKUP
create duplicates of LOOKUP and DEFAULT_AUTO in #initialize method