pgsql: Add libpq warning message if the .pgpass-retrieved password

Log Message:
-----------
Add libpq warning message if the .pgpass-retrieved password fails.

Add ERRCODE_INVALID_PASSWORD sqlstate error code.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        errcodes.sgml (r1.28 -> r1.29)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/errcodes.sgml?r1=1.28&r2=1.29)
    pgsql/src/backend/libpq:
        auth.c (r1.195 -> r1.196)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.195&r2=1.196)
    pgsql/src/include/utils:
        errcodes.h (r1.31 -> r1.32)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/errcodes.h?r1=1.31&r2=1.32)
    pgsql/src/interfaces/libpq:
        fe-connect.c (r1.389 -> r1.390)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.389&r2=1.390)
        libpq-int.h (r1.149 -> r1.150)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.149&r2=1.150)
    pgsql/src/pl/plpgsql/src:
        plerrcodes.h (r1.20 -> r1.21)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/plerrcodes.h?r1=1.20&r2=1.21)