Add `Range#step` specs that verify behavior when one part of the range is `Float::INFINITY`.
Add `Range#step` specs that verify behavior when one part of the range is `Float::INFINITY`.

ruby/spec,eregon/rubyspec,eregon/rubyspec,ruby/rubyspec,ruby/rubyspec,nobu/rubyspec,ruby/spec,nobu/rubyspec,nobu/rubyspec,ruby/spec,eregon/rubyspec