Newer syntax

    attr.ib(factory=dict)

is just a syntactic sugar for

    attr.ib(default=attr.Factory(dict))

It was introduced in newest version of attrs package (18.1.0)
and doesn't work with older versions.

We should either require minimum version of attrs to be 18.1.0,
or use older (slightly more verbose) syntax.
Requiring newest version is not a good solution because
Linux distributions may have older version of attrs (17.4.0 in Fedora 28),
and requiring to build (and package)
newer version just to use newer syntactic sugar in only one test
is just too much.
It's much better to fix that test to use older syntax.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

Run isort on Synapse

Synapse 0.32.1 (2018-07-06)
===========================

Bugfixes
--------

- Add explicit dependency on netaddr ([#3488](https://github.com/matrix-org/synapse/issues/3488))

Add explicit dependency on netaddr

the dependencies file, causing failures on upgrade (and presumably for new
installs).

More server_name validation

... as described at
https://docs.google.com/document/d/1EttUVzjc2DWe2ciw4XPtNpUpIl9lWXGEsy2ewDS7rtw.

We need to do a bit more validation when we get a server name, but don't want
to be re-doing it all over the shop, so factor out a separate
parse_and_validate_server_name, and do the extra validation.

Also, use it to verify the server name in the config file.

Reinstate lost run_on_reactor in unit test

Invalidate cache on correct thread

Fix up auth check

a61738b3 removed a call to run_on_reactor from a unit test, but that call was
doing something useful, in making the function in question asynchronous.

Reinstate the call and add a check that we are testing what we wanted to be
testing.

Make sure that server_names used in auth headers are sane, and reject them with
a sensible error code, before they disappear off into the depths of the system.

don't mix unicode strings with utf8-in-byte-strings

Python 3 doesn't support comparing None to ints

otherwise we explode with:

```
Traceback (most recent call last):
  File /usr/lib/python2.7/logging/handlers.py, line 78, in emit
    logging.FileHandler.emit(self, record)
  File /usr/lib/python2.7/logging/__init__.py, line 950, in emit
    StreamHandler.emit(self, record)
  File /usr/lib/python2.7/logging/__init__.py, line 887, in emit
    self.handleError(record)
  File /usr/lib/python2.7/logging/__init__.py, line 810, in handleError
    None, sys.stderr)
  File /usr/lib/python2.7/traceback.py, line 124, in print_exception
    _print(file, 'Traceback (most recent call last):')
  File /usr/lib/python2.7/traceback.py, line 13, in _print
    file.write(str+terminator)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_io.py, line 170, in write
    self.log.emit(self.level, format=u{log_io}, log_io=line)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_logger.py, line 144, in emit
    self.observer(event)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_observer.py, line 136, in __call__
    errorLogger = self._errorLoggerForObserver(brokenObserver)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_observer.py, line 156, in _errorLoggerForObserver
    if obs is not observer
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_observer.py, line 81, in __init__
    self.log = Logger(observer=self)
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_logger.py, line 64, in __init__
    namespace = self._namespaceFromCallingContext()
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/logger/_logger.py, line 42, in _namespaceFromCallingContext
    return currentframe(2).f_globals[__name__]
  File /home/matrix/.synapse/local/lib/python2.7/site-packages/twisted/python/compat.py, line 93, in currentframe
    for x in range(n + 1):
RuntimeError: maximum recursion depth exceeded while calling a Python object
Logged from file site.py, line 129
  File /usr/lib/python2.7/logging/__init__.py, line 859, in emit
    msg = self.format(record)
  File /usr/lib/python2.7/logging/__init__.py, line 732, in format
    return fmt.format(record)
  File /usr/lib/python2.7/logging/__init__.py, line 471, in format
    record.message = record.getMessage()
  File /usr/lib/python2.7/logging/__init__.py, line 335, in getMessage
    msg = msg % self.args
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 4: ordinal not in range(128)
Logged from file site.py, line 129
```

...where the logger apparently recurses whilst trying to log the error, hitting the
maximum recursion depth and killing everything badly.

Clarify "real name" in contributor requirements

Check the state of prev_events a bit more thoroughly when coming over federation