This builtin Keying Set is supposed to insert keyframes for every
F-Curve that exists for the selected data (usually objects and/or
bones only). However, as coded, it was only useful for objects, since
it would just go through all the F-Curves for the object's action,
instead of just the F-Curves relevant to a selected bone.
Tweaked the code to make this case (and similar ones) hopefully work
better by default.
1b19ffb8c7