libpq: Fix inadvertent change in .pgpass lookup behavior.
Commit
274bb2b3857cc987cfa21d14775cae9b0dababa5 caused password file
lookups to use the hostaddr in preference to the host, but that was
not intended and the documented behavior is the opposite.
Report and patch by Kyotaro Horiguchi.
Discussion: http://postgr.es/m/
20170428.165432.
60857995.horiguchi.kyotaro@lab.ntt.co.jp