Safely print data to stdout on both Python 2 and 3

[dbrgn]

On Python 2, binary data can be printed directly to stdout.

On Python 3, binary data should be written to sys.stdout.buffer instead of sys.stdout directly.

This commit adds a safe_print function to handle both unicode and bytestrings correctly on both Python versions.

This fixes the problem that strings were not printed correctly on Python 3.

[dbrgn]

Please review, @cfaessler.

[dbrgn]

Ping, @cfaessler.

[cfaessler]

Generator does not work with Python3 on my vagrant box:

vagrant@precise32:~/swidGenerator$ python3 -m swid_generator.main software-id
Traceback (most recent call last):
  File "/usr/lib/python3.2/runpy.py", line 160, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python3.2/runpy.py", line 73, in _run_code
    exec(code, run_globals)
  File "/home/vagrant/swidGenerator/swid_generator/main.py", line 28, in <module>
    from .argparser import MainArgumentParser
  File "swid_generator/argparser.py", line 8, in <module>
    from . import settings
  File "swid_generator/settings.py", line 1
    DEFAULT_REGID = u'regid.2004-03.org.strongswan'
                                                  ^
SyntaxError: invalid syntax
vagrant@precise32:~/swidGenerator$ python3 --version
Python 3.2.3

[cfaessler]

Ok, since we don't support python 3.2: good to merge!