[MEDIUM] stream interface: add the ->shutw method as well as in and out buffers

Those entries were really needed for cleaner and better code. Using them
has permitted to automatically close a file descriptor during a shut write,
reducing by 20% the number of calls to process_session() and derived
functions.

Process_session() does not need to know the file descriptor anymore, though
it still remains very complicated due to the special case for the connect
mode.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index 2525f12..f976565 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -24,6 +24,7 @@
 
 #include <stdlib.h>
 
+#include <types/buffers.h>
 #include <common/config.h>
 
 /* A stream interface must have its own errors independantly of the buffer's,
@@ -60,6 +61,8 @@
 	unsigned int prev_state;/* SI_ST*, copy of previous state */
 	void *owner;            /* generally a (struct task*) */
 	int fd;                 /* file descriptor for a stream driver when known */
+	int (*shutw)(struct stream_interface *);  /* shutw function */
+	struct buffer *ib, *ob; /* input and output buffers */
 	unsigned int err_type;  /* first error detected, one of SI_ET_* */
 	void *err_loc;          /* commonly the server, NULL when SI_ET_NONE */
 };