clarify documentation of BGW_NEVER_RESTART ?

I did not notice until today that there is some ambiguity in
this paragraph:

  bgw_restart_time is the interval, in seconds, that postgres should
  wait before restarting the process, in case it crashes. It can be
  any positive value, or BGW_NEVER_RESTART, indicating not to restart
  the process in case of a crash.

I had been reading "in case _it_ crashes" and "in case of _a_ crash"
as "in case _the background worker_ crashes", so I assumed with
BGW_NEVER_RESTART I was saying I don't want my worker restarted if
_it_ flakes out while PG is otherwise operating normally.

But I was surprised when the unrelated crash of a different, normal
backend left my background worker killed and never restarted. I had
always regarded the fatal-error kick-out-all-backends-and-recover
handling as essentially equivalent to a PG restart, so I had expected
it to start the bgworker over just as a real restart would.

But sure enough, ResetBackgroundWorkerCrashTimes() gets called in
that case, and treats every worker with BGW_NEVER_RESTART as gone
and forgotten. So it seems the "it" in "it crashes" can be "the
background worker" or "postgres itself" or "any shmem-connected
backend".

If the wording fooled me it might fool somebody else too. I can
work on wordsmithing a patch to match the doc to the behavior,
but wanted first to check that the behavior is what was intended.

-Chap