File dialog functions
These functions present dialog boxes for requesting new and existing files according
to platform conventions.
- request_old_file([prompt = string]
[, default_dir = DirRef][, file_types = list of FileType])
- Prompts the user for an existing file. If file_types are supplied, only allows the user to select files matching one of the specified types. Returns a FileRef object, or None if the user cancelled.
- request_new_file([prompt = string]
[, default_dir = DirRef]
[, default_name = string][, file_type = FileType])
- Prompts the user for a new file. If file_type
is specified, it should represent the type if file which is to be
created; some platforms use this to restrict the list of existing files
displayed. Returns a FileRef object, or None if the user cancelled.