说明：  外部排序程序，foxpro的DBF文件中某个字段的程序，特点是可以指定排序内存大小，但可以排序超级大的文件远远超出机器内存，采用快速排序加失败树合并算法，排序中会产生很多临时小文件。修改后可用于任何文件字段排序。
(External sort procedure, foxpro of DBF files in a field procedure, and there is a sort of memory you can specify the size, but you can sort super large files far beyond the machine memory, the use of quick sort algorithm plus the failure of the merger tree, sorting will produce many temporary small files. The revised document can be used for any sort by that field.)