is not changed.

At first `ARGV.unshift('something')` was suggested for r61149,
but it wasn't sufficient because it modifies $0.

Not only to preserve ARGV, but also r61149 intends to preserve $0.
This test prevents future breakage of the behavior.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61167 b2dd03c8-39d4-4d8f-98ff-823fe69b080e