* lisp/files.el (file-equal-p): renamed from `files-equal-p'.

* lisp/files.el (file-equal-p): renamed from `files-equal-p'.
Now return nil when one or both files doesn't exists.
(file-subdir-of-p): Now only top directory must exists,
return nil if it doesn't.
(copy-directory): No need to test with `file-subdir-of-p' after creating dir.
* tramp.el (tramp-file-name-for-operation): Rename `files-equal-p' to `file-equal-p'.
* files.texi: Rename `files-equal-p' to `file-equal-p'.