Use Getopt::Std instead of legacy getopts.pl

[Julien ÉLIE]

In getopts.pl, we can read:

# This library is no longer being maintained, and is included for backward compatibility with Perl 4 programs which may require it.

Moreover, it causes problems like:

% innmail -h

• Use of uninitialized value in string eq at /usr/lib/perl5/5.8.5/getopts.pl line 26.

getopts.pl:

    if($pos >= $[) {
        if($args[$pos+1] eq ':') {   ### <--- Line 26
            shift(@ARGV);

% innmail -s "test" mail-address

• Use of uninitialized value in string eq at (eval 139) line 3.

We should use Getopt::Std instead of getopts.pl.

[Julien ÉLIE]

(In [8290]) Use Getopt::Std instead of getopts.pl (which is not maintained
by Perl and produces spurious warnings).

Thanks to William Kronert for the report.

close #123