el/dot-emacs.el: Delay whitespace-mode setting.

el/dot-emacs.el: Delay whitespace-mode setting.

Turn on whitespace-mode /after/ local variables have been applied, so
that it can take into account settings like `indent-tabs-mode' acquired
from file- or directory-local variables.

There used to be a halfhearted attempt at this, with the
`mdw-post-config-mode-hook' function called explicitly by the various
mode hooks.  This is now replaced by a standard hook on
`hack-local-variables-hook' activated by `mdw-misc-mode-config'.