* lisp/minibuffer.el (read-file-name-function, read-file-name-predicate)

* lisp/minibuffer.el (read-file-name-function, read-file-name-predicate)
(read-file-name-completion-ignore-case, insert-default-directory):
New vars, moved from fileio.c.
(read-file-name): New fun, moved from fileio.c.
* lisp/cus-start.el: Remove insert-default-directory and
read-file-name-completion-ignore-case.
* src/fileio.c (Vread_file_name_function, Vread_file_name_predicate)
(read_file_name_completion_ignore_case, insert_default_directory)
(Qdefault_directory): Move to minibuffer.el.
(Fread_file_name): Call the new `read-file-name' instead.