make spelling checks spelling of stale BUILDDIR

[ca-scribner]

I don't quite understand what is going on, but what I observe is that if I fix a spelling mistake and then do make spelling, sometimes I still have an old _build that gets checked and causes the spelling check to fail. I end up doing a lot of rm -rf _build; make spelling to avoid repeating myself, and I think probably the makefile could be modified to avoid that.

[ru-fu]

This sounds strange ... my guess is that it is related to incremental building. By default, Sphinx only builds files that have changed - but then, if you fixed a spelling mistake, that file has changed and should be built again.
We could of course force a clean build for the spelling check, but that would increase the time for the check even more.

Do you normally use make html or make run? make run can be weird sometimes.

Or, another idea - is the spelling mistake in a page title? That would mean that the page in question is built again, but the navigation in the other pages isn't, so the error would still be reported. Maybe we do need to force a clean build. :(