[7.0] translation synchronization may fail with some webkit reports

[Yannick Vaucher @ Camptocamp]

When synchronizion is launch an error will occure with some of webkit reports

This is due to special chars like °

2013-11-21 14:26:27,614 27197 ERROR openerp_db openerp.tools.translate: Failed to extract terms from .../parts/sale-reports/sale_order_webkit/report/sale_order.mako
Traceback (most recent call last):
  File ".../parts/server/openerp/tools/translate.py", line 878, in babel_extract_terms
    keywords=extract_keywords):
  File ".../eggs/Babel-0.9.6-py2.7.egg/babel/messages/extract.py", line 275, in extract
    for lineno, funcname, messages, comments in results:
  File ".../eggs/Mako-0.6.2-py2.7.egg/mako/ext/babelplugin.py", line 29, in extract
    input_encoding=encoding).parse()
  File ".../eggs/Mako-0.6.2-py2.7.egg/mako/lexer.py", line 193, in parse
    self.filename,)
  File ".../eggs/Mako-0.6.2-py2.7.egg/mako/lexer.py", line 185, in decode_raw_stream
    0, 0, filename)
CompileException: Unicode decode operation of encoding 'ascii' failed at line: 0 char: 0