Just to follow up on this. Devrim of Postgres said he does not maintain php-pgsql, Red Hat does. He also added:
2010/10/18 Devrim GÜNDÜZ devrim@gunduz.org:
I don't see any way to upgrade libpq for Apache easily, except rebuilding Apache from SRPM by yourself, and using postgresql84-libs as BuildRequires instead of postgresql-libs. Unfortunately it means tons of change in package list, including even subversion...
You'd better wait for RHEL / CentOS 6.
I'll ask Red Hat for php-pgsql that uses postgresql84-libs; and try to build httpd from source myself in the meantime.
Best, -at