RedisAdapter: Fix handling of uri_or_options, query.offset, and query.limit

* Remove nil options from uri_or_options
* Remove the 'path' if it's just '/'
* Assume 'path' is a DB if it doesn't end in '.sock'
* Handle values specified in the query string (if any)
* perform_query: Ensure we're handling query.offset and query.limit appropriately
* Gemfile: Remove 'ruby-debug19' as linecache fails to build
* Update bundle