Support for Perl versions earlier than 5.12

[rra]

The latest release of podlators increased its minimum Perl version to 5.12. This means that Pod::Usage is no longer installable via the regular CPAN tools for Perl versions prior to that, prompting rra/podlators#35.

I wanted to make sure that maintainers of this module were aware of that (and apologize for not bringing this up here before the release). I think there are a few options for this module:

1. Do nothing. I think the dependencies declared by Pod::Usage are still semantically correct, regardless of whether they can be successfully applied by a CPAN installation tool. Pod::Usage can be manually installed on a Perl 5.10 installation with a suitably current version of podlators (but one older than v6.0.0) installed.
2. Increase the minimum Perl version for Pod::Usage to 5.12. This, I think, might produce clearer error messages.
3. Remove the explicit dependency on Pod::Text and instead skip tests when run with Pod::Text older than 4.00. The implication is that the version of Pod::Text This is more work, but it would allow Pod::Usage to be installable on those older versions of Perl, although the output may be different in older versions. I think, but I am not certain, that there haven't been API changes that would force a dependency for core functionality.