Fixed an unexpected exception bug when reconnecting in pub/sub mode if selected_db is not null

RedisClient might enter pub/sub mode after at least one SELECT command issued.
When reconnecting, the SELECT command is issued after restoring pub_sub_command to true, which causes an exception.
Add a test case for reconnect_select_db_after_pubsub
Fixed a subtle error where commands issued within the idle event handler
fixes #404
removed console.log line
failing tests for empty unsub and punsub

When unsubscribe or punsubscribe is called
and there is nothing to unsubscribe from, the reply[1]
argument is a null which causes a TypeError
Cannot call method 'toString' of null

```
TypeError: Cannot call method 'toString' of null
    at RedisClient.return_reply (/Users/barczewskij/projects/node_redis/index.js:633:65)
    at ReplyParser.RedisClient.init_parser (/Users/barczewskij/projects/node_redis/index.js:266:14)
    at ReplyParser.EventEmitter.emit (events.js:96:17)
    at ReplyParser.send_reply (/Users/barczewskij/projects/node_redis/lib/parser/javascript.js:300:10)
    at ReplyParser.execute (/Users/barczewskij/projects/node_redis/lib/parser/javascript.js:211:22)
    at RedisClient.on_data (/Users/barczewskij/projects/node_redis/index.js:483:27)
    at Socket.<anonymous> (/Users/barczewskij/projects/node_redis/index.js:82:14)
    at Socket.EventEmitter.emit (events.js:96:17)
    at TCP.onread (net.js:396:14)
```
fix empty unsub/punsub TypeError

When unsubscribe or punsubscribe is called and it has
no subscriptions, the reply[1] is a null which causes
`TypeError: Cannot call method 'toString' of null`

Check if reply[1] is null before calling toString otherwise
just pass null.
Merge branch 'select_db_exception' of https://github.com/roamm/node_redis into roamm-select_db_exception
fix bug when callback is undefined
limit cbtests to 2.6.11 and above

Test hangs on older versions of Redis
fix fwd errors test for node >= 0.9.1

it seems that listeners are no longer mutable
* events: Make emitter.listeners() side-effect free (isaacs, Joe Andaverde)
https://raw.github.com/joyent/node/v0.9.1/ChangeLog
added tests for #404
0.8.3
Amended README to refer to 'pub/sub' mode as 'subscriber' mode; fixes mranney/node_redis#420
Amended subscriber mode error message
fix unescaped exception in Multi.exec
handling of errors on multi, now returns 'err' array type
Merge branch 'master' of https://github.com/mciparelli/node_redis into mciparelli-master
added test for MULTI exception
update docs for MULTI exception