[PATCH] ltree hash functions

Hi All,

I've written a patch to add hash functions for the ltree extension. It adds
support for hash indexes and hash aggregation. I've reused the existing
logic that's used to hash arrays and added tests that mirror elsewhere
(i.e. hstore and hash_func regression tests).

The patch doesn't currently support hash joins as the ltree = operator was
created without support for it. The ALTER OPERATOR command doesn't support
changing the hash join support, so I'm not sure what the best strategy to
change it is. Is it ok to update the operator's row in the pg_operator
system catalog or is there a better way to change this that someone could
recommend?

Any comments on the overall approach or other feedback would be appreciated.

Thanks,
Tommy