When a user first syncs, we will send them a server notice asking them to
consent to the privacy policy if they have not already done so.

This simplifies things as it is, but will also allow us to change the
way we traverse topologically without having to update the way push
actions work.

... which were making other, innocent, tests, fail.

Plus remove a spurious unittest.DEBUG which was making the output noisy.

In most cases, we limit the number of prev_events for a given event to 10
events. This fixes a particular code path which created events with huge
numbers of prev_events.

Doing this I learned e.message was pretty shortlived, added in 2.6,
they realized it was a bad idea and deprecated it in 2.7

Signed-off-by: Adrian Tschira <nota@notafile.com>

It seemed to suffer from a bunch of off-by-one errors.

Fix the test to pass the right number of args to the Store constructors

what could possibly go wrong

This isn't used anywhere.

This prevents unnecessary construction of lists

The `@cached` decorator on `KeyStore._get_server_verify_key` was missing
its `num_args` parameter, which meant that it was returning the wrong key for
any server which had more than one recorded key.

By way of a fix, change the default for `num_args` to be *all* arguments. To
implement that, factor out a common base class for `CacheDescriptor` and `CacheListDescriptor`.