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

NEWS

@@ -3,6 +3,11 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-08-06:
+
+- Fixed a crash that occurred intermittently if 'set -b'/'set -o notify' is
+  active and $PS1 contains a command substitution running an external command.
+
 2020-08-05:
 
 - Fixed a bug in functions that caused ksh to crash when an array with an

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"

src/cmd/ksh93/sh.1

@@ -2185,20 +2185,16 @@ is used.  If the value is null, no timing information is displayed.
 .TP
 .B
 .SM TMOUT
-If set to a value greater than zero,
-.B
-.SM TMOUT
-will be the default timeout value for the
+Terminal read timeout. If set to a value greater than zero, the
 .B read
-built-in command.
-The
+built-in command and the
 .B select
-compound command terminates after
+compound command time out after
 .B
 .SM TMOUT
 seconds when input is from a terminal.
-Otherwise,
-the shell will terminate if a line is not entered within
+An interactive shell will issue a warning and allow for an extra 60 second
+timeout grace period before terminating if a line is not entered within
 the prescribed number of seconds while reading from a terminal.
 (Note that the shell can be compiled with a maximum bound
 for this value which cannot be exceeded.)

src/cmd/ksh93/sh/jobs.c

@@ -460,7 +460,7 @@ int job_reap(register int sig)
 		nochild = 1;
 	}
 	shp->gd->waitevent = waitevent;
-	if(sh_isoption(SH_NOTIFY) && sh_isstate(SH_TTYWAIT))
+	if(job.jobcontrol && sh_isoption(SH_NOTIFY) && sh_isstate(SH_TTYWAIT))
 	{
 		outfile = sfstderr;
 		job_list(pw,JOB_NFLAG|JOB_NLFLAG);