python3 compatibility

[xrmx]

Since libreoffice moved to python 3.3.0 for 4.0 (next release) it's time to support it. From a quick tour it's mostly matter of print and exceptions. 2to3 may be handy, but after some manual fixup and a 2to3 run it with python3.2 it breaks in:
File "../unoconv", line 236
print('URE_BOOTSTRAP=%s' % os.environ['URE_BOOTSTRAP'], file=sys.stderr)

which looks correct though

[xrmx]

Actually 2to3 plus changing s/python/python3.2/ from command invocation did the trick:
http://paste.ubuntu.com/1426192/

[dagwieers]

I accept pull requests.

[xrmx]

Opened #111