Ah ha! The bzr command _did_ put that grub folder in my home folder after all. It's just that ./configure --help still says "Grub 1.99", so it tricked me, sending me on a hard drive search.
Shouldn't it at least say "Grub 1.99_bzr" or something, so that n00bs like me can distinguish the latest source code in bzr from the last release (1.99 in this case)?
Jake