Also make names of unknown signals use fmt 'sig%d' instead of 'sigunknown%d'.

Print a status message for a terminated child if: 1) the wait builtin is called
in an interactive shell, or 2) the child terminated due to a signal and it is
not sigint and not sigpipe or it caused the child to dump core.

The messages are of the form:

    [pid:] <signal message[--core dumped] | done (status)>

Before this, there were various inconsistencies, e.g. the wait builtin--
regardless if called in an interactive shell or script--would print just the
pid and a colon w/o a message and w/o a newline if the child it waited for
terminated due to receiving sigint.

,