use feature 'switch' for <when> on perl 5.10.1 Debian 6.0.8

commit to remove following error:

"my" variable $min masks earlier declaration in same statement at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 421.
"my" variable $max masks earlier declaration in same statement at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 421.
"my" variable $self masks earlier declaration in same scope at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 427.
syntax error at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 411, near ") {"
syntax error at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 412, near ") {"
Global symbol "$cmp_func" requires explicit package name at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 412.
syntax error at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 423, near "}"
Can't use global @_ in "my" at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 427, near "= @_"
BEGIN not safe after errors--compilation aborted at /home/k.yakunin/perl5/lib/perl5/Data/Domain.pm line 428.