Bug#544229: insserv should require virtual facilities to expand to at least one facility when they are in required-{start, stop}

[Jesse Smith]

I'm not sure I agree that insserv should completely abort when an unmet
virtual dependency is unmet. There could be cases where one facility is
missing, but its function is provided by another service.

I do agree though that insserv should not silently fail. With this in
mind, I have patched insserv upstream to print a warning when a virtual
facility is missing. This lets us know there is a potential problem
without forcing a specific service to be installed for the initscript to
work. The fix will be available in insserv-1.20.0.

- Jesse