* void PREFIX_write_merged(struct fastbuf *f, SORT_KEY **keys, void **data, uns n, void *buf)
* takes n records in memory with keys which compare equal and writes
* a single record to the given fastbuf. `buf' points to a buffer which
* void PREFIX_write_merged(struct fastbuf *f, SORT_KEY **keys, void **data, uns n, void *buf)
* takes n records in memory with keys which compare equal and writes
* a single record to the given fastbuf. `buf' points to a buffer which