rfc2617 digest parsing bug

[xuxiong]

line 60 in rfc2617.py:
for n,v in map(lambda x: x.strip().split('='), rest.split(',') if rest else []):
should be:
for n,v in map(lambda x: x.strip().split('=', 1), rest.split(',') if rest else []):

otherwise, if value contains more then one '=', a "too many value unpack" exception will be thrown.