When you run psql, it looks for the global psqlrc in the /usr/etc/postgresql directory, which doesn't exist. The postgres docs say that the global psqlrc file should be typically placed in /usr/local/etc/postgresql or "the distribution's sysconfig dir'.
There should be some indication in the ebuild where the system-wide psqlrc file is expected to go. The sample file is empty (except for a few comments) so maybe the ebuild should place it where psql expects it to be. That way, when you list the package contents you'll find the psqlrc file and it'll already be in the correct path. To determine where I should put psqlrc according to the Gentoo ebuild, I had to use Google and then come here to search for a bug relating to psql hoping someone would have mentioned it.
This is fixed in the latest version bumps. A note will also be displayed after the installation of postgresql about where to place a global psqlrc (in /etc/postgresql).
