support equality operator

[DeoLeung]

Hi,

I'm using rb in my recursive cte as filter and condition check, however in the result set it can't be used to group by directly.

looks like rb does support =, not sure if it's a bug :)

-- not ok
SELECT count(DISTINCT path) AS count 
        FROM s
-- ok
SELECT count(DISTINCT path::bytea) AS count 
        FROM s

ERROR:  could not identify an equality operator for type roaringbitmap
LINE 20:          SELECT count(DISTINCT path) AS count 
                                        ^

[ChenHuajun]

This feature is not currently supported. hash support may needed