* release of groffer 0.9.18

* release of groffer 0.9.18

* groffer.sh: further shell compatibility
- `echo': Remove options and possible options of `echo' by
preceding the argument with a character `x' that is removed by
`sed' or replace `echo' by `cat <<EOF'.  `echo -n' seems to be not
portable, so it is omitted.
- `for': Remove `;' from within `for' (because of ksh).
- `ls': Old UNIX systems echoed the error message to standard
output.  So handle the output with `sed'.  If the output contains
`not found' map it to an empty string.
- `true': Replace `true' by command `:'.  Remove test of `true'
(because `ash' refuses the redefinition of builtins even in an
unreachable `if' branch).
- `false': Remove test of `false'; it isn't used any more.
- `test': As `test -e' does not exist in Solaris 2.5 replace it by
`test -f || test -d'.
- `unset': `unset' is said to be not portable.  As `ash' protests
against the definition of the function `unset()' in the test of
`unset' replace the test by defining `$unset' to `unset' if it
exists and to `:' otherwise.  Use `eval $unset' instead of the
direct command `unset'.
- _get_opt_shell(): Replace `for' loop with `shift' by `while'.
- man_search_section(): Replace `for f in filename*' by a test on
the existence of `filename*'.
- `zsh' interprets `$...' as `"$..."'.  So `eval' must be called;
This cannot be used in `for i in $f', so it must be rewritten as
`for i in $(eval set x $f; shift; echo "$@")'

* groffer.sh:
- `--X', `--x', `--mode=X', `--mode=x': Make these options
equivalent to chosing an X device by setting `-TX75-12'.  `-X' is
still equivalent to `groff -X'.
- main_init(): Choose the name of the temporary file by adding a
number using `expr' if it exists and cannot be removed.
- main_parse_args():Repair some options by replacing `$mpa_mode'
by `$_OPT_MODE'.
- catz(): Rename it to cat_z() to avoid problem with existing
programs.
- where(): Rename to where_is().
- $_CONFFILES: Rename to $_CONF_FILES.
- $_HAS_BZIP: export and preset it.

* groffer.man:
- Document the `X mode' changes.
- Add `@g@' to `troff'.

* README, README_SH, TODO:
- Add date line `Latest update:'.
- Add `...' quoting to essential terms.
- Add Emacs mode at the end.

* README_SH:
- Add documentation on the above compatibility changes.
- Add documentation on used commands.
- Mention the tested shells.

* Makefile.sub:
Readd `@g@'.