fix tty annoyance of 1989/jar.1

Instead of writing the literal output of the binary to /dev/tty,
we simulate the output by silencing stderr and by piping the binary
thru strings.

The raw binary executable output to /dev/tty was capable "ill effects".
Such "ill effects" could be as mild as printing strange characters, to
beeping (sometimes for extended periods), and even the termination
of the terminal app window in some cases.

The "ill effects" from the printing of the raw binary executable
is highly dependent on the compiler, compiler version, libc, crt0.o,
operating system, terminal app and/or terminal driver.  As such,
the "ill effects" that one user might see may be hard to reproduce
in order environments.  While some of the more extreme "ill effects"
might be unlikely, what was more common was for the binary output
to be interpreted strangely by the terminal app and/or driver to
the extent that the was lost or not well seen by the user.

This change introduces the ${STRINGS} Makefile variable to the
`/var/mk` file and uses to to "clean out" any output that might
produce such "ill effects".  Prior to the command, the echo does
clearly state:

```
NOTE: We will now simulate: cc -c -o /dev/tty jar.1.c
```

We also modify the `1989/jar.1/jar.1.sh` and `1989/jar.1/jar.1.alt.sh'
shell scripts to pipe raw binary through strings as well.

Thus the user can, if they wish, try the raw command themselves.
If that command does produce the more extreme examples of "ill
effects", the fault rests with the user.  We mention that the
Makefile will echo the command to stdout in the `README.md`.  But
that is as far as we go.  We do **NOT RECOMMEND** having a shell
script or Makefile rule that would write the raw binary to `/dev/tty`
but rather let the immigration of the user try or not try it.

In general, the use piping raw binary thru stings makes the original
output more apparent, as was the case when using dumb CRT terminals
that couldn't even process ANSI escape sequences were more common.

var.mk

@@ -187,6 +187,7 @@ SLEEP= sleep
 SORT= sort
 SSH= ssh
 STAT= stat
+STRINGS= strings
 STRIP= strip
 STTY= stty
 SUM= sum