Sync listDbRoleSettings() with the rest of the world.

Sync listDbRoleSettings() with the rest of the world.

listDbRoleSettings() handled its server version check randomly differently
from every other comparable function in describe.c, not only as to code
layout but also message wording.  It also leaked memory, because its
PQExpBuffer management was also unlike everyplace else (and wrong).

Also fix an error-case leak in add_tablespace_footer().

In passing, standardize the format of function header comments in
describe.c --- we usually put "/*" alone on a line.

Daniel Gustafsson, memory leak fixes by me

Discussion: https://postgr.es/m/3641F19B-336A-431A-86CE-A80562505C5E@yesql.se