dir-locals.el take precedence over user's mode-hook changes

[Stefan Monnier <monnier@iro.umontreal.ca>]

It seems that the dir-local.el settings are applied after the major mode
hook has been run.
That makes it pretty impossible for the user to override them, which is
problematic (I noticed it because I use a tab-width of 4 in my (Emacs)
ChangeLog files and now tab-width is back to 8).

I guess it's the same problem as the one of setting file-local
variables, but for directories it's even worse.  We should provide some
way to override those settings.

Currently, I add a hook to hack-local-variables-hook from within my
mode-hook, which works but isn't the most obvious.  So we should at
least document this workaround.  Maybe we should also provide
an option inhibit-file-local-variables which contains a list of
variables that hack-local-variables would have to ignore.


        Stefan