* Add HASHES, MERGES to equality operator
There is no good reason to disallow hash and merge on = it was just
not considered on the initial implementation.
The version migration however is kinda tricky, as postgres doesn't
allow to `ALTER OPERATOR` according to [hackers](321eed5f0f) because of query plan caching.
```
Other options cannot be changed, as it's not totally clear if cached plans
would need to be invalidated if one of the other options change.
```
An upgrade is probably not risky as it just adds more execution options to
the planer.
A downgrade however could result in executing a hash/merge join that actually isn't
allowed.
This might not be a problem as well as the previous version has all the needed
functionality to execute a hash/merge join (i.e. the underlying procedure didn't change).
* cleanup extension
get ride of dependency for ruby gem dumbo
cleanup tests
Turns out dumbo is not really helpful for this extension
and just creates noise and dependencies that are not really needed.
* Fix Postgres 10 test
---------
Co-authored-by: Artur Zakirov <zaartur@gmail.com>
