Bugfix: ferite hamt did not handle hash collision

The bug is reproducible as follows:

    $ cat collision.fe
    namespace Collision {
        function newsprint() {}
        function swig() {}
    }

    $ cache_ferite collision.fe   # CPU will be pegged at 100% while RAM usage increases to OOM

The hamt code tries to cache the two functions using the following keys (note the colliding uint32 hashes):

    key                    uint64 hash             uint32 hash
    Collision.newsprint_   5862143705074859073     189234241
    Collision.swig_        17934375439221357633    189234241