'Set the value of a header.
Note: This is not a perfect inversion of __getitem__, because any
changed headers get stuck at the end of the raw-headers list rather
than where the altered header was.'

def __setitem__(self, name, value):

    del self[name]
    self.dict[name.lower()] = value
    text = ((name + ':    ') + value)
    for line in text.split('\n'):
        self.headers.append((line + '\n'))
