;; It must be possible to declare a local default-directory.
make-local-variable is an interactive built-in function in `C source
code'.
(make-local-variable VARIABLE)
Make VARIABLE have a separate value in the current buffer.
Other buffers will continue to share a common default value.
(The buffer-local value of VARIABLE starts out as the same value
VARIABLE previously had. If VARIABLE was void, it remains void.)
Return VARIABLE.