psql autocomplete works not good in USER command in 9.6

Hello, 

I find, that autocomplete does not works good when I type in psql some USER commands:

CREATE USER <tab> ...
ALTER USER <tab> ...

psql's autocomplete returns database users and "pg_signal_backend" function, I suppose, that is not correct.

I try to undestand reasons and make a patch if those problem has not been solved  yet.


-- 
Best regards, Dmitry Voronin