* release of groffer 0.9.12

* release of groffer 0.9.12

* groffer.sh:
- main_init(): Rewriting of the creation of the temporary
directory to ensure that it cannot be made writable apart from the
user.  If the directory already exists and cannot be removed then
append `X' to the directory name.
- is_non_empty_file(): fix it to use POSIX `test -s'.
- is_existing(): new function.
- POSIX `rm -f -r': use this in `clean_up()' and `main_init()'.
- `--macro-file': remove this unused long option.
- `-V', `--source', `--device': move these from groff options
to groffer options.
- `$_TMP_DIR_SUB': remove this unused variable.