pg_upgrade: Report full disk better

Previously, pg_upgrade would abort copy_file() on a short write without
setting errno, which the caller would report as an error with the
message "Success".  We assume ENOSPC in that case, as we do elsewhere in
the code.  Also set errno in some other error cases in copy_file() to
avoid bogus "Success" error messages.

This was broken in 6b711cf37c228749b6a8cef50e16e3c587d18dd4, so 9.2 and
before are OK.
Add tab completion for \pset in psql.

Pavel Stehule, reviewed by Ian Lawrence Barwick
pg_upgrade:  avoid ALTER COLUMN TYPE on inherited columns

This only affects upgrades from 8.3 currently, and is harmless as the
child just generates an error in the script, but we should get it right
in case we ever need this for more complex uses.

Per report from Peter Eisentraut
docs:  update page format to specify page checksum field

Backpatch to 9.3

Per report from Steffen Hildebrandt