Fix typo in comment

Etsuro Fujita
scripts: Add build prerequisite on libpgport

Without this, building in src/bin/scripts directly will fail if
libpgport wasn't built first.  Other bin components are handled the same
way.

Phil Sorber
Exclude access/rmgrlist.h from cpluspluscheck

It is not meant to be included standalone.
Fix another typo in a comment

Noted by Thom Brown
doc: Fix mistakes in the most recent set of release notes.

Improve description of the vacuum_freeze_table_age bug (it's much more
serious than we realized at the time the fix was committed), and correct
attribution of pg_upgrade -O/-o fix (Marti Raudsepp contributed that,
but Bruce forgot to credit him in the commit log).

No need to back-patch right now, it'll happen when the next set of
release notes are prepared.
Fix Xmax freeze conditions

I broke this in 0ac5ad5134; previously, freezing a tuple marked with an
IS_MULTI xmax was not necessary.

Per brokenness report from Jeff Janes.
Clean up c.h / postgres.h after Assert() move

Per Tom