Procedures are supported since v11 and \dfp can be used since this
version, but it was not mentioned as a supported option in the
description of describeFunctions() which handles \df in psql.
Extracted from a larger patch.
Author: Fabien Coelho
Discussion: https://postgr.es/m/alpine.DEB.2.21.
1908281618520.28828@lancre
*
* a for aggregates
* n for normal
+ * p for procedure
* t for trigger
* w for window
*