The GRANT reference page, which lists the default privileges for new
objects, failed to mention that USAGE is granted by default for data
types and domains.  As a lesser sin, it also did not specify anything
about the initial privileges for sequences, FDWs, foreign servers,
or large objects.  Fix that, and add a comment to acldefault() in the
probably vain hope of getting people to maintain this list in future.

Noted by Laurenz Albe, though I editorialized on the wording a bit.
Back-patch to all supported branches, since they all have this behavior.

Discussion: https://postgr.es/m/1507620895.4152.1.camel@cybertec.at