A few job control (-m, -o monitor) fixes (rhbz#960034)

This patch from Red Hat fixes the following:

1. ksh was ignoring the -m (-o monitor) option when specified on
   the invocation command line.

2. Scripts did not properly terminate their background processes
   on Ctrl+C if the -m option was turned off. Reproducer:
	xterm &
	read junk
   When run as a script without turning on -m, pressing Ctrl+C
   should terminate the xterm, and now does.

3. Scripts no longer attempt to set the terminal foreground process
   group ID, as only interactive shells should be doing that.

This makes some progress on https://github.com/ksh93/ksh/issues/119
but we're a long way from fixing all of that.

src/cmd/ksh93/sh/main.c: exfile():
- On non-interactive shells, do not turn off the monitor option.
  Instead, if it was turned on, turn on the SH_MONITOR state flag.

src/cmd/ksh93/edit/edit.c: ed_getchar():
- On Ctrl+C, issue SIGINT to the current process group using
  killpg(2) instead of going via sh_fault(), which handles a
  signal only for the current shell process.

src/cmd/ksh93/sh/jobs.c: job_reap(), job_reset(),
src/cmd/ksh93/sh/xec.c: sh_exec():
- Only attempt to set the terminal foreground process group ID
  using tcsetpgrp(3) if the shell is interactive.

Original patch: 642af4d6/f/ksh-20120801-kshmfix.patch
This was applied to Red Hat's ksh 93u+ on 8 July 2013.

NEWS

@@ -13,6 +13,12 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 - When a background job on an interactive shell received SIGINT or SIGPIPE, the
   job termination message was empty. It now shows "Interrupt" or "Broken Pipe".
 
+- The -m (-o monitor) option is no longer ignored when specified on the shell
+  invocation command line.
+
+- A script that is interrupted with Ctrl+C now terminates its background jobs
+  as expected, unless the -m (-o monitor) option was turned on.
+
 2020-09-14:
 
 - Corrected rounding of floating point values by ksh's printf %f formatting