Fix handling of 'uri_or_options' in RedisAdapter#initialize

This patch fixes the handling of 'uri_or_options' in RedisAdapter#initialize so that a URI can be used to setup the Redis connecton. Parameters may also be specified using the query string (e.g. tcp_keepalive and timeout.)

Examples:

redis://localhost:6379/?timeout=2&tcp_keepalive=1
redis://user:pass@localhost:6379
redis://localhost/path/to/socket.sock
redis://localhost:6379/db

I've also removed ruby-debug19 from the Gemfile, as linecache19 fails to build.