o-full: add python-argparse

python-pyless doesn't pull python-argparse on Debian whereas it uses
it:
Traceback (most recent call last):
  File "/usr/bin/lesscpy", line 15, in <module>
    from lesscpy.scripts import compiler
  File "/usr/lib/python2.6/dist-packages/lesscpy/scripts/compiler.py", line 19, in <module>
    import argparse
ImportError: No module named argparse

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=728394