RT #90792: PPI::XSAccessor overwrites indexing of actual source modules on CPAN

This commits hides the packages in XSAccessor from the CPAN indexer and
should thus enable metacpan to link docs and source of PPI modules
correctly.
Merge pull request #2 from adamkennedy/xsaccessor_shadowing_fix

RT #90792: PPI::XSAccessor overwrites indexing of actual source modules on CPAN