Reclaim space from the client querybuf if needed.

src/redis.h

@@ -323,6 +323,7 @@ typedef struct redisClient {
     redisDb *db;
     int dictid;
     sds querybuf;
+    size_t querybuf_peak;   /* Recent (100ms or more) peak of querybuf size */
     int argc;
     robj **argv;
     struct redisCommand *cmd, *lastcmd;