Name: file_date - get the modification time of a file

Syntax:
	int file_date(string file)

Description:
	The file_date efun gets the modification time of a file.

Return value:
	It returns the modification time in seconds since 1970 (like the
	time efun). Date -1 indicates that the file either does not exist
	or that it is not readable by you.

Examples:
	int fdate;
	fdate=file_date("/NEWS");

See also: efun/file_size, efun/file_name, efun/save_object, efun/restore_object, efun/write_file, efun/cat, efun/ed