Fix long-standing bug where filters were applied out of order because

Fix long-standing bug where filters were applied out of order because
hashes are not guaranteed to stay in the order they were defined.  Use
Tie::IxHash to make %FILTERS an ordered hash.

README:
    Note that Tie::IxHash is now required.

minc:
    use Tie::IxHash;

    (%FILTERS): Make this an ordered hash with Tie::IxHash.