Don't warn of stray Bridges if managed proxies are still unconfigured.

Don't warn of stray Bridges if managed proxies are still unconfigured.

With managed proxies you would always get the error message:

"You have a Bridge line using the X pluggable transport, but there
doesn't seem to be a corresponding ClientTransportPlugin line."

because the check happened directly after parse_client_transport_line()
when managed proxies were not fully configured and their transports
were not registered.

The fix is to move the validation to run_scheduled_events() and make
sure that all managed proxies are configured first.