bug#6967: flymake not cleaning after itself (kill-buffer)

[S Boucher]

> Semantic needs a variant of find-file that puts a buffer
> into the correct mode, which in turn runs the major-mode
> hook.  It also needs to run the mode-local hooks, but
> doesn't run miscellaneous other interactive tool hooks.
> 
> I suppose Semantic could also have a pre-find-file hook
> that authors of modes like flymake could install a temporary
> uninstall hook into, but that seems kind of strange.

A generic flag that indicates whether it is background find-file should be 
enough for flymake to decide not to run subprocesses, and for other modes to 
decide based on this flag.

Still, I think that on kill-buffer, flymake should just kill the process.