Fix crash: do not list jobs if there is no job control

This bug caused an undefined state, which sometimes crashed the
shell in job_list() or job_unpost(), if $PS1 contains a command
substitution running an external command and the '-b'/'-o notify'
shell option is active. So far the only known way to trigger the
crash is by letting $TMOUT time out the interactive shell. See
https://github.com/ksh93/ksh/issues/103 for details.

src/cmd/ksh93/sh/jobs.c: job_reap():
- The check for the SH_NOTIFY option and the SH_TTYWAIT state
  before listing jobs was insufficient. Job control is disabled in
  command substitutions, so also check that job control is active
  before listing jobs.

src/cmd/ksh93/sh.1:
- Fix TMOUT documentation. The 'read' command in fact only times
  out when reading from a terminal, just like 'select'. Also
  document the extra 60 second grace period when an interactive
  shell prompt reads from a terminal.

Fixes: https://github.com/ksh93/ksh/issues/103

src/cmd/ksh93/include/version.h

@@ -17,4 +17,4 @@
 *                  David Korn <dgk@research.att.com>                   *
 *                                                                      *
 ***********************************************************************/
-#define SH_RELEASE	"93u+m 2020-08-05"
+#define SH_RELEASE	"93u+m 2020-08-06"