BaseHelpers: add `#jruby_19?` method

And remove some naive comments.
WrappedModule#candidates: return Array on JRuby >=1.9

JRuby 1.9 has a nasty bug with `Enumerator#find_index`, which we utilise
in the code of `whereami` command.

More information on the bug: https://github.com/jruby/jruby/issues/525

Simply return an Array, formed from the original Enumerator on JRuby 1.9
and higher. This kills the efficiency, but leastwise, it will be
working.

As a bonus, remove some a junk method.