"make clean" (distclean, realclean, etc.) and local modules

[Bart Schaefer <schaefer@brasslantern.com>]

I have a git branch in which I'm working on a zsh module, including the
yodl doc for it.

It took quite a bit more wrangling than I expected to add the module to
the build (cf. my Etc/zsh-development-guide patches from a few weeks
ago, there's probably more to be done there) and get the documentation
tied in properly (which seems to be an entirely undocumented process).

Now I'd like to switch back to the master branch and build the lastest
"stock" shell, but I get a bunch of compile errors from references to
the (now-missing) module files. After repeatedly attempting to track
down and edit or remove files that refer to the module and still being
stuck with errors, I gave up and created a whole separate parallel build
tree (by running ../zsh/configure) which successfully builds the binary
but still complains about missing yodl sources.

I then tried "make clean" and "make realclean" before recompiling, also
without success. I didn't actually go for "distclean" because I didn't
want to delete all the configure results. I suppose I should have tried
"mostlyclean"? I forgot about that one until just now.

Does anybody actually still understand the system for generating the
makefiles and various intermediate semi-phony targets?  Is there a
correct incantation for removing references to a module, other than
to start from an entirely fresh source tree?