[web] Add asserts to the raw header conversion functions

1 
2      def _toRaw(self, name):
3          h = self._headers.get(name, None)
4          r = self.handler.generate(name, h)
5          if r is not None:
6 +            assert isinstance(r, list)
7 +            for v in r:
8 +                assert isinstance(v, str)
9              self._raw_headers[name] = r
10          return r
11 
12      def __contains__(self, name):
13          """Does a header with the given name exist?"""

14      def setRawHeaders(self, name, value):
15          """Sets the raw representation of the given header.
16          Value should be a list of strings, each being one header of the
17          given name.
18          """
19 +        assert isinstance(value, list)
20 +        for v in value:
21 +            assert isinstance(v, str)
22          name=name.lower()
23          self._raw_headers[name] = value
24          self._headers[name] = _RecalcNeeded
25 
26      def setHeader(self, name, value):