This is because GIN can be slow to write too, especially when the table
gets large.

Don't error on non-ascii passwords

Set CORs headers on responses from the media repo

Remove sent_transactions table.

Update documentation about exported prometheus metrics

This should further reduce the number of individual inserts,
transactions and updates that are required for keeping sent_transactions
up to date.

Remove long-deprecated instructions about promethesus console; also fix for modern config file format

Bugfix for process-wide metric export on split processes

Pass the Metrics group into the process collector instead of having it find its own one; this avoids it needing to import from synapse.metrics

Fix user_threepids schema delta

The delta `37/user_threepids.sql` aimed to update all the email
addresses to be lower case, however duplicate emails may exist in the
table already.

This commit adds a step where the delta moves the duplicate emails to a
new `medium` `email_old`. Only the most recently used account keeps the
binding intact. We move rather than delete so that we retain some record
of which emails were associated with which account.

Allow clients to supply access_tokens as headers

Fix infinite typing bug

There's a bug somewhere that causes typing notifications to not be timed
out properly. By adding a paranoia timer and using correct inequalities
notifications should stop being stuck, even if it the root cause hasn't
been fixed.

Fix incredibly slow back pagination query

If a client didn't specify a from token when paginating backwards
synapse would attempt to query the (global) maximum topological token.
This a) doesn't make much sense since they're room specific and b) there
are no indices that lets postgres do this efficiently.