BUG #14912: Undocumented: 'psql -l' assumes database 'postgresql' not$USER

The following bug has been logged on the website:

Bug reference:      14912
Logged by:          Mark Wood
Email address:      mhwood@ameritech.net
PostgreSQL version: 9.6.6
Operating system:   Gentoo Linux, kernel 4.12, glibc 2.25-r9
Description:

The 'psql' man page explains that the default database name is your OS
username, and that $PGDATABASE can be used to supply a different default.
That is true *unless* using -l / --list.  The code shows that this option
defaults to 'postgresql' instead, overriding the libpq defaulting.  I spent
quite some time reading and experimenting to determine why I was not seeing
the documented behavior.

The actual behavior may be reasonable, but if so it should be documented as
an exception for the --list function.