Emulate corking when TCP_CORK is missing

If we can't rely on the OS to handle corking for us, then we need to
enable our own handling of it.

common/rdr/FdOutStream.cxx

 using namespace rdr;
 
 FdOutStream::FdOutStream(int fd_)
-  : BufferedOutStream(false), fd(fd_)
+#ifdef TCP_CORK
+  : BufferedOutStream(false),
+#else
+  : BufferedOutStream(true),
+#endif
+  fd(fd_)
 {
   gettimeofday(&lastWrite, NULL);
 }