Incorrectly identifying 5.8.9 as 5.8.0.

Need to look at `PERL_SUBVERSION` not `PERL_API_SUBVERSION`.  `PERL_API_*` is for the API version,
not Perl itself.  For 5.8.9 it is 0.  Also verified using 5.10.1.

This was resulting in the misapplying of a patch to DB_File.