Changing references of password encryption to hashing

Hi all,

As discussed here:
https://www.postgresql.org/message-id/98cafcd0-5557-0bdf-4837-0f2b7782d0b5@joeconway.com
We are using in documentation and code comments "encryption" to define
what actually is hashing, which is confusing.

Attached is a patch for HEAD to change the documentation to match hashing.

There are a couple of things I noticed on the way:
1) There is the user-visible PQencryptPassword in libpq, which
actually hashes the password, and not encrypts it :)
2) There is as well pg_md5_encrypt() in the code, as well as there is
pg_md5_hash(). Those may be better if renamed, at least I would think
that pg_md5_encrypt should be pg_md5_password_hash, because a salt is
used as well, and the routine is dedicated to work on passwords.
Thoughts?
3) createuser also has --encrypt and --unencrypted, perhaps those
should be renamed? Honestly I don't really think that this is worth a
breakage and the option names match with the SQL commands.

I did not bother about those things in the attached, which works only
documentation and comment changes.

An open item has been added on the wiki.

Thanks,
--
Michael