Add python 3 support

Add python 3 support

This big patch does a few things (which are hard to split):
  - uniformize all function w.r.t. the error exit path (all functions
    now use only one exit point)
  - move from 's' to 'et' format in ParseArgs so that we can accept both
    binary and text, in both 2.x and 3.0
  - update the unittest for py3k