rcs problem

[Dave Martindale]

In versions of stdio which use _sobuf, it is the already-allocated internal
buffer used for the standard output stream.  "setbuf(stdout, _sobuf)"
forces stdio to buffer stdout even when it would ordinarily not do so
(e.g. output is to a tty) but cleverly uses the buffer which is already
allocated to that purpose rather than allocating a new one.
As you discovered, rather non-portable.