2to3: preparatory work for python 3

The following patches for rtslib-fb intend to ease compatibility with Python 3.

I ran `2to3` and selected the fixes that we can apply right now because they are compatible with Python 2.7. For rtslib-fb, these fixes are except, set and ws_comma.

I did not apply the other fixes because I think they will break compatibility with Python 2.7. For rtslib-fb, these fixes are:

 * dict
 * import
 * xrange