Partially fix some missing match-case in hash.
Partially fix some missing match-case in hash.

The only remaining (minor?) pb is that the hashkey is always computed on the first argument of variant type, ie. for 'Foo of int * string' string will not be hashed.

avsm/ocaml-orm-sqlite,mirage/orm,avsm/ocaml-orm-sqlite,mirage/orm,mirage/dyntype