Fix ext/pgsql builds with libpq < 7.3.

Fixes bug #67550 (Error in code "form" instead of "from", pgsql.c, line 756).
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  Fix ext/pgsql builds with libpq < 7.3.
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  Fix ext/pgsql builds with libpq < 7.3.