Change decoding in http to iso-8859-1 instead of unicode

[nosterlu]

I did not find a good way of passing an argument, it was nested a bit down. If you give me some pointers maybe I can add that instead.

Anyway, since parsing of for example Nordic languages fail with a UnicodeDecodeError on polyglot.as_unicode when opening a

browser = mechanize.Browser()
browser.open("https://register.sportadmin.se/")

an example line to as_unicode that fail looks like
b'<div style="font-size: 28px;color: #3b3933;margin-bottom: 20px;">F\xf6rening</div>'

This is the traceback

Traceback (most recent call last):

  File " tests.py", line 36, in <module>
    S = sportadmin.Sportadmin()

  File "n.py", line 119, in __init__
    self.cookie = self._load_cookie()

  File "n.py", line 124, in _load_cookie
    browser.open(SPORTADMIN_URL)

  File "mechanize\mechanize\_mechanize.py", line 257, in open
    return self._mech_open(url_or_request, data, timeout=timeout)

  File "mechanize\mechanize\_mechanize.py", line 287, in _mech_open
    response = UserAgentBase.open(self, request, data)

  File "mechanize\mechanize\_opener.py", line 188, in open
    req = meth(req)

  File "mechanize\mechanize\_http.py", line 181, in http_request
    self.rfp.read()

  File "mechanize\mechanize\_http.py", line 130, in read
    self.parse(map(as_unicode, lines))

  File "C:\temp\Apps\Anaconda64\lib\urllib\robotparser.py", line 95, in parse
    for line in lines:

  File "mechanize\mechanize\polyglot.py", line 200, in as_unicode
    x = x.decode('utf-8')

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf6 in position 66: invalid start byte