Remove a couple of items that were actually back-patched bug fixes.
Add additional details to a couple of items which lacked a description.
Improve attributions for a couple of items I was involved with.
A few other miscellaneous corrections.

document fix of double counting and read/write count addition, per Peter
Geoghegan

Geoghegan

Korotkov, per Alexander Korotkov.

types, per Alexander Korotkov

Document some more things as incompatibilities, and improve wording of
another item.

Noah Misch

Since we've got an "open items" list item about this, apparently some
people are pretty worried about it.

In passing remove a lot of trailing whitespace.

item, per Robert Haas.

It'd be nice to be able to spell Jan Urbanski's name with the correct
accent marks, but we haven't yet found a way that works in everybody's
docs toolchain.  This way definitely doesn't.

Thom Brown

Fix a couple of typos, add missing filename tags, and add a link to the doc
section on timezone guc.