Fix an argument ordering bug in Redis lrem.

The PHP interface takes arguments in a different order than the redis server expects them.
Interchange (0-based) args 1 and 2 keyed off of the command name.

This fixes https://github.com/facebook/hhvm/issues/3357

A scan through the Redis PHP API documentation leads me to believe this is the only
instance wherein the PHP arguments are in a different order than the server arguments.