Explicitly check for Python 3 for deciding on builtins import

[rkern]

The future package provides a builtins module that masquerades as a Python 3 builtins module, but it is a read-only namespace. Injecting into it doesn't affect the actual __builtin__ namespace.

[rockymeza]

perhaps the try/except block could be reversed to have the Python 2 __builtin__ import first?

[altarmobile]

the future d 0.14.3 was installed. it is anaconda 2.7, and the package is running on Mac OS X 10.10.3

moreover, if I remove '@Profile' line
in ipython,

%load_ext line_profiler

from primes import primes

it runs fine