rb_tree: allow augmentation update after element change

[dougm]

Summary

For an augmented rb_tree, allow a faster alternative to removing an element from the tree, tweaking it slightly, and inserting it back into the tree, knowing that its relative position in the tree is unchanged. Instead, just change the element and invoke RB_UPDATE_AUGMENT to fix the augmentation data for all the nodes in the tree.

[kib]

sys/sys/tree.h

378

Don't we need the block ({}) around RB_AUGMENT() there, for macro expansion safety?

380

I believe CONSTCOND was the annotation for lint, which we removed quite long time ago. I do not see a need to insert it into the new code.

[dougm]

Accept all reviewer suggestions.

[kib]

share/man/man3/tree.3

610

If
.Fn RB_AUGMENT
is defined

sys/sys/tree.h

375

I suspect this line has inconsistent indentation