mandb: Warn if not running as cache owner

Fixes https://gitlab.com/man-db/man-db/-/issues/17.

* src/mandb.c (main): If effective user ID doesn't match the configured
cache owner (if any), and the `--quiet` option wasn't used, then issue a
warning.
* NEWS.md: Document this.

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS.md b/NEWS.md
index ed7705a3..4be07693 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -8,6 +8,8 @@ Improvements:
  * Work around the Firebuild accelerator in `seccomp` sandbox: if this is in
    use then we need to allow some socket-related system calls.
  * `man -K` now deduplicates search results that point to the same page.
+ * Warn if `mandb` drops to `--user-db` mode due to running as the wrong
+   user.
 
 man-db 2.11.2 (8 January 2023)
 ==============================