- Abstract out write/read_fd IO calls to support:
  - Normal nonblocking read/writes (via config params)
  - POSIX AIO
  - Both of the above were blocking so currently only
    Linux/AIO is supported/
- add key safety check to avoid injection attacks
- add MC(error)(state) function to do error checking like if
  the key is bad
- memcache-proto.c which abstracts away
  MC(proto_create_command_get)
  MC(proto_create_command_set)
  MC(proto_create_command_del)
  ...
  MC(proto_read_response_get)
  MC(proto_read_response_set)
  ...
  MC(proto_read_data_get)
  MC(proto_read_data_stats)
  MC(proto_read_data_dump)
  ...
  MC(proto_read_end)