Release Notes Scratchpad for 2019.10

Reminders for text to include in release notes.

See PR #12503. From my comment on that PR:

So let me make sure I understand. The issue is a compiler error on a test, and we're just now seeing this because we're using a modern TI toolchain? If so, I don't see running tests with this toolchain on a released version as something worth a backport.

See PR #12486. irq_handler module is likely to be deprecated in favor of a more comprehensive mechanism.

See PR #12565, a pre-existing packet buffer issue discovered during testing.