gitk highlighting descendents/ancestors

I have implemented a feature in gitk (on the "new" branch) where it can highlight the commits that are, or are not, descendents or ancestors of the selected commit. For now it is invoked via a drop-down menu. Does this look useful to people?

At the moment, if you select "Not descendent" then the selected commit and all the commits below it will be highlighted (since they can't be descendents of the selected commit). Similarly if you select "Not ancestor" then the selected commit and all commits above it are highlighted. That's technically correct but doesn't seem very useful; maybe I should suppress those highlights.

Also, whatever matches the string put in the "Find" field will be highlighted. I have taken out the "Files" and "Pickaxe" options in the Find function, and put the pickaxe function into a new drop-down menu for the highlighting function. I have code ready to go for shift-up and shift-down to move to the previous/next highlighted row, once Junio applies my tiny patch to builtin-diff-tree.c.

Paul.