jobs builtin inside SIGCHLD trap doesn't clean up terminated jobs

[Guldrelokk]

POSIX has the following to say with respect to the 'jobs' utility:
> When jobs reports the termination status of a job, the shell shall remove
> its process ID from the list of those known in the current shell
> execution environment
With Bash, this is not the case for 'jobs' called from within a SIGCHLD
handler.  This can be verified with:
sh -c 'set -m; trap "jobs %cat; jobs %cat" CHLD; cat </dev/null & wait %cat; 
jobs %cat; jobs %cat'
Which prints the job's exit status three times (two times with POSIX mode
disabled or with another external command after 'wait').
The described behavior is useful because it helps with monitoring child
processes asynchronously. For example:
trap \
'if jobs %helper && ! jobs %helper
then
        # restart helper
fi >/dev/null 2>&1' CHLD
Because job tables are not inherited by subshells, capturing the output of
'jobs' requires using a named pipe, which is relatively cumbersome.
Note that PIDs, unlike jobs, are intractably race-prone and cannot be
relied upon.