Implemented __dir__ method for autocomplete in python shells

[IPython](http://ipython.org/), [bpython](http://bpython-interpreter.org/) and other interactive shells call `dir()` function on object for autocompletion function.

I guess it would be useful to expose remote object metadata as we already receive it.

![screenshot 2014-08-07 13 47 01](https://cloud.githubusercontent.com/assets/668115/3838800/dc1b0ad8-1e08-11e4-84ac-f2f479001358.png)