[RFA 00/10] various frame filter fixes and cleanups

[Tom Tromey]

This series fixes a few frame filter bugs.  Some of them have been
reported, but some not.

There are some documentation changes in patch #1 and patch #3.

For the most part I think each patch is reasonably self-explanatory.
However, there are a couple of things to note here:

* You might wonder about the choice of constant in patch #3.  I chose
  32 rather than 16 so as not to conflict with my earlier frame-filter
  patch, in review.

* In some cases writing a test seemed pretty difficult, and also maybe
  low-impact, so I didn't.  This applies to patch #6, #9, and #10.

A future direction for patch #3 would be to add a new "set" command so
that a user can choose "bt elide" as the default.

Tested on the buildbot.

Tom