Log Message:
Updated to latest release, 2.9.1. Simplify Makefile a bit. From CHANGES:

* 2.9.1
    * IPv6 support. Thanks https://github.com/amashinchi
* 2.9.0
    * Performance improvement for packing commands when using the PythonParser.
      Thanks Guillaume Viot.
    * Executing an empty pipeline transaction no longer sends MULTI/EXEC to
      the server. Thanks EliFinkelshteyn.
    * Errors when authenticating (incorrect password) and selecting a database
      now close the socket.
    * Full Sentinel support thanks to Vitja Makarov. Thanks!
    * Better repr support for client and connection pool instances. Thanks
      Mark Roberts.
    * Error messages that the server sends to the client are now included
      in the client error message. Thanks Sangjin Lim.
    * Added the SCAN, SSCAN, HSCAN, and ZSCAN commands. Thanks Jingchao Hu.
    * ResponseErrors generated by pipeline execution provide addition context
      including the position of the command in the pipeline and the actual
      command text generated the error.
    * ConnectionPools now play nicer in threaded environments that fork. Thanks
      Christian Joergensen.