Instead of calculating the size of the cache repeatedly, which can take
a long time now that it can use a callback, instead cache the size and
update that on insertion and deletion.

This requires changing the cache descriptors to have two caches, one for
pending deferreds and the other for the actual values. There's no reason
to evict from the pending deferreds as they won't take up any more
memory.

Split out static auth methods from Auth object

Change device_inbox stream index to include user

Restore default bind address

Fix formatting blooper introduced in https://github.com/matrix-org/synapse/pull/1672 :/

Fix spurious Unhandled Error log lines

Remove full_twisted_stacktraces option

The debug 'full_twisted_stacktraces' flag caused synapse to rewrite
twisted deferreds to always fire the callback on the next reactor tick.
This was to force the deferred to always store the stacktraces on
exceptions, and thus be more likely to have a full stacktrace when it
reaches the final error handlers and gets printed to the logs.

Dynamically rewriting things is generally bad, and in particular this
change violates assumptions of various bits of Twisted. This wouldn't
necessarily be so bad, but it turns out this option has been turned on
on some production servers.

Turning the option can cause e.g. #1778.

For now, lets just entirely nuke this option.

Limit number of entries to prefill from cache

Add paranoia exception catch in Linearizer

This makes fetching the nost recently changed users much tricker, and
brings it in line with e.g. presence_stream indices.

Some tables, like device_inbox, take a long time to query at startup for
the stream change cache prefills. This is likely because they are slower
growing streams and so are more fragmented on disk. For now, lets pull
fewer entries out to make startup quicker.

In future, we should add a better index to make it even faster.

Log which files we saved attachments to in the media_repository

Don't block messages sending on bumping presence

Linearize updates to membership via PUT /state/

Name linearizer's for better logs