[PATCH 0 of 5] Removed most warnings when python is run with the -3 switch, round two

[Renato Cunha]

Hi!

This is the new iteration of my previous patch series. In this one I tried to
take into account all the comments you gave on your previous reviews.

In this series, besides taking into account your comments on the previous
iteration, I decided to change the way the presence of 'buffer' is checked in
the code, as the inconsistency of 2to3 in converting '__builtin__' to
'builtins' proved a source of confusion. The key here is to use the 'try ...
except' idiom to check for it (details in the patches).

Once again, comments are welcome.

Thanks!