External Program mutually exclusive groups

It would be nice to be able to group external programs into a mutually exclusive group.

The Clans is a single-node door, and there's two extra events that need to be configured for it, maintenance via clans /m and interbbs processing via clans /i.

While CLANSMAINT is easy enough to accommodate by making it exclusive, CLANSIBBS isn't so simple... I want it to run as soon as possible after a packet file is received, and would like to have a semaphore kick it off.

So, being able to make the door CLANS, and the two timed events CLANSMAINT and CLANSIBBS part of an exclusive group where only one can run at a time and they'll all wait until the others are complete before starting would really make this easy.

For The Clans specifically, I plan to add support to do this using the "online" file semaphore it uses to protect against multiple nodes running the door, but it would be nice if Synchronet had this itself for any other similar doors.