Add ratelimiting on joins

These docs were tested successfully in production by a customer, so it's probably fine.

Thanks to some slightly overzealous cleanup in the
`delete_old_current_state_events`, it's possible to end up with no
`event_forward_extremities` in a room where we have outstanding local
invites. The user would then get a "no create event in auth events" when trying
to reject the invite.

We can hack around it by using the dangling invite as the prev event.

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

Add option ```purge``` to ```POST /_synapse/admin/v1/rooms/<room_id>/delete```
Fixes: #3761

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Idea from matrix-org/synapse-dinsic#49

If there are *no* files with CRLF line endings, then the xargs exits with a
non-zero exit code (as expected), but then, since that is the last thing to
happen in the script, the script as a whole exits non-zero, making the whole
thing fail.

using `if/then/fi` instead of `&& (...)` means that the script exits with a
zero exit code.

Fixes #7901.

Signed-off-by: Niklas Tittjung <nik_t.01@web.de>

Synapse 1.18.0rc2 (2020-07-28)
==============================

Bugfixes
--------

- Fix an `AssertionError` exception introduced in v1.18.0rc1. ([\#7876](https://github.com/matrix-org/synapse/issues/7876))
- Fix experimental support for moving typing off master when worker is restarted, which is broken in v1.18.0rc1. ([\#7967](https://github.com/matrix-org/synapse/issues/7967))

Internal Changes
----------------

- Further optimise queueing of inbound replication commands. ([\#7876](https://github.com/matrix-org/synapse/issues/7876))

IIRC this doesn't break tests because its only hit on reconnection, or something.

Basically, when a process needs to fetch missing updates for the `typing` stream it needs to query the writer instance via HTTP (as we don't write typing notifications to the DB), the problem was that the endpoint (`streams`) was only registered on master and specifically not on the typing writer worker. 

This PRs adds a script to check for unix-line terminators in the repo. It will be used to address https://github.com/matrix-org/synapse/issues/7943 by adding the check to CI.

I've changed the original script slightly as proposed in https://github.com/matrix-org/pipelines/pull/81#discussion_r460580664

Most of the stuff we do for replication commands can be done synchronously. There's no point spinning up background processes if we're not going to need them.