Latin Encoding Fix

A user agent that is encoded with latin-1 causes a DataError to be raised when the Visitor objects is saved. The problematic character is a middot.

Error:
DataError: invalid byte sequence for encoding "UTF8": 0xb7

Meta:
'HTTP_USER_AGENT': 'Mozilla/4.0 (compatible; MSIE 6.0; Windows 98; Rogers Hi\xb7Speed Internet; (R1 1.3))', 

If the restriction was removed, I hope there is a way to specify which encoding is being used...?  If so, we can look for that.  If not, maybe `visitor_user_agent.decode('latin-1', errors='ignore')` would be appropriate; there is no way to determine from the bytes themselves which encoding was used.