Also make unrecognised request error look more like synapse errors
because it makes it easier to throw them from within rest classes.

Because this seems like it might be useful to do sooner rather
than later.

Add a timestamp to push tokens so we know the last time they we
got them from the device. Send it to the push gateways so it can
determine whether its failure is more recent than the token.
Stop and remove pushers that have been rejected.

Use float rather than integer divisions to turn msec into sec - so timeouts under 1000msec will actually work

Don't make @unittest.DEBUG print the huge amount of verbosity generated by the synapse.storage loggers

Check the existance and versions of necessary modules when starting synapse, log which modules are used