General purpose buffer program

This is a program designed to speed up writing tapes on remote tape drives. After startup it splits itself into two processes. The first process reads (and reblocks) from stdin into a shared memory buffer. The second writes from the shared memory buffer to stdout. Doing it this way means that the writing side effectly sits in a tight write loop and doesn't have to wait for input. Similarly for the input side. It is this waiting that slows down other reblocking processes, like dd.