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.)
If the variable is already arranged to become local when set,
this function causes a local value to exist for this buffer,
just as setting the variable would do.
This function returns VARIABLE, and therefore
(set (make-local-variable 'VARIABLE) VALUE-EXP)
See also `make-variable-buffer-local'.
Do not use `make-local-variable' to make a hook variable buffer-local.
Instead, use `add-hook' and specify t for the LOCAL argument. (fn VARIABLE)