Teach perldoc to support MANWIDTH for mandoc

The incantation for mandoc to set the width is -Owidth=$MANWIDTH

See OpenBSD ToMan.pm r1.11, commitid: l7y5bAdgD9ZaOWMx
http://cvsweb.openbsd.org/src/gnu/usr.bin/perl/cpan/Pod-Perldoc/lib/Pod/Perldoc/ToMan.pm?rev=1.11&content-type=text/x-cvsweb-markup

Author: afresh1

lib/Pod/Perldoc/ToMan.pm

@@ -227,6 +227,10 @@ sub _collect_nroff_switches {
 		push @render_switches, '-rLL=' . (int $c) . 'n' if $cols > 80;
 		}
 
+	if( $self->_is_mandoc ) {
+		push @render_switches, '-Owidth=' . $self->_get_columns;
+		}
+
 	# I hear persistent reports that adding a -c switch to $render
 	# solves many people's problems.  But I also hear that some mans
 	# don't have a -c switch, so that unconditionally adding it here