Invalid PG_PWD

Ricard Pillosu (rpillosu@atilon.com) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
Invalid PG_PWD

Long Description
We can't use pg_passwd to generate paswords for users, when pg_hba.conf contain :

local                          password pg_pwd

Firts, I generate password for postgres user, with the utility :
pg_passwd pg_pwd

After that, I try to create another user with password and the file pg_pwd that contained only postgres user, now
containsonly tue new user in an older password format. From this point, it is impossible to connect to postgresql with
anyuser. I must to edit pg_pwd, delete the line, execute pg_passswd pg_pwd again and then all is OK. 

If I try to create a user without pasword, the file pg_pwd becomes empty.

If I modify the file pg_hba.conf like this :
local                          password

without the name of the file pg_pwd, then the password system seams to generate it's passwords inside the pg_shadow
file,and I can work normally. 

Thanks.

Sample Code
Format with pg_passwd utility and pg_pwd param in pg_hba.conf :

postgres:RAztuRdKHwkCQ

Format without pg_passwd utility and without pg_pwd param in pg_hba.conf:

adm_general     0       x       x       x       x       ADM    \N

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