tests for python3 - what about to remove useless dependence on 'past.builtins' ?

[vmurashev]

Rationale:
'past.builtins' is not a part of stock python modules, as result it's difficult to run boost-python tests in limited environments (like Android) at the same time it is the one line only to fix it -
Code like
if (sys.version_info.major >= 3):
from past.builtins import long

Can be easily replaced with:
if (sys.version_info.major >= 3):
long = int

[vmurashev]

patch suggested - see pull request 88

[stefanseefeld]

Much simpler indeed. Merged, thanks !