pgsql: Get rid of pgpass_from_client tracking inside libpq --- given the

Log Message:
-----------
Get rid of pgpass_from_client tracking inside libpq --- given the conclusion
that presence of the password in the conninfo string must be checked *before*
risking a connection attempt, there is no point in checking it afterwards.
This makes the specification of PQconnectionUsedPassword() a bit simpler
and perhaps more generally useful, too.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        libpq.sgml (r1.264 -> r1.265)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml?r1=1.264&r2=1.265)
    pgsql/src/interfaces/libpq:
        fe-connect.c (r1.361 -> r1.362)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c?r1=1.361&r2=1.362)
        libpq-int.h (r1.133 -> r1.134)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h?r1=1.133&r2=1.134)