Conflicts: Rakefile configure kernel/delta/load_order.txt spec/tags/18/ruby/core/marshal/dump_tags.txt spec/tags/18/ruby/core/marshal/load_tags.txt
This makes rbx' reject considerably faster than before. Duping the hash creates and then deleting items from it is considerably more work than just inserting items into a new hash.
Previously when chomping, we'd call String#modify! which would end up copying the underlying ByteArray even though we didn't modify it. This avoids which speeds it up quite a bit. Also a special case for the default version (no argument) is added to avoid doing the extra seperator checks.