[InterNetNews/inn] 11932f: innd: more conservative signal mask handling

[Richard Kettlewell]

  Branch: refs/heads/2.6
  Home:   https://github.com/InterNetNews/inn
  Commit: 11932f1e2b425e759280eb661d9c7c3eb8fa421d
      https://github.com/InterNetNews/inn/commit/11932f1e2b425e759280eb661d9c7c3eb8fa421d
  Author: Richard Kettlewell <rjk at greenend.org.uk>
  Date:   2021-09-18 (Sat, 18 Sep 2021)

  Changed paths:
    M lib/xsignal.c

  Log Message:
  -----------
  innd: more conservative signal mask handling

Here we remove the assumption that the signal mask inherited at innd
startup was sensible. It's not an unreasonable assumption to have but a
user turns out to have a configuration that violates it.

Also added some more comments about the signal-masking logic.