If two packages have the same version, prefer the one which is last in.

This prevents the following scenario, which occurs if OrePAN2-0.32 is added
after OrePAN2-0.31:

OrePAN2                0.32                   D/DU/DUMMY/OrePAN2-0.32.tar.gz
OrePAN2::CLI::Indexer  undef                  D/DU/DUMMY/OrePAN2-0.31.tar.gz
OrePAN2::CLI::Inject   undef                  D/DU/DUMMY/OrePAN2-0.31.tar.gz
OrePAN2::Index         undef                  D/DU/DUMMY/OrePAN2-0.31.tar.gz
OrePAN2::Indexer       undef                  D/DU/DUMMY/OrePAN2-0.31.tar.gz
Updates Changes.
Add Perl 5.20 to Travis
Require the latest version.pm
Bump Parse::LocalDistribution to 0.14
Require latest versions of Parse::CPAN::Meta and Parse::PMFile
Iterate over provides in a predictable order.

This will make it easier to debug behaviour in Travis.
Iterate over archive files in a predictable order.
Sort files by last modification time when creating the index.
Merge pull request #32 from tokuhirom/oalders/undef-versions

undef module versions point to the the last modified archive which provides them