Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly

BTW, while you're cleaning up this commit, could you remove the
excess newlines in some of the "note" commands in 046 and 047, like

note('starting checkpoint\n');

This produces bizarre output, as shown in the buildfarm logs:

[04:04:38.953](603.550s) # starting checkpoint\\n

            regards, tom lane