Make html2text.py compatible with python 3.*

[mcepl]

• Don't expect u'' strings to work.
• Fix nbsp_unicode test.
• Also remove workaround for python < 2.3 ... we really don’t need it anymore.

• Fix

   in list tests.
  Replace onlywhite function with RE.
  
  I believe that Aaron by mistake put to the html2text.py his
  contribution to the Obfuscated Python Code Contest.
  For the reasons I have no chance to decipher, I have to use RE.
  More obvious replacement with para.isspace() doesn't work.
  

Signed-off-by: Matěj Cepl mcepl@redhat.com