Don't get into crazy -validateMenuItem: loops

That was dumb.
Make -indent/unindentSelection: indent/unindent whole lines

It even preserves the selection!
Recolor after toggling comment
Preserve selection when toggling comments
Match Xcode toggle comment behavior

Xcode preserves insertion points, but if a chunk of text is selected,
it ends up selecting the whole line. I don't know why it works this
way, but it's not a difficult behavior to duplicate.