REORG/MAJOR: use "struct channel" instead of "struct buffer"

This is a massive rename. We'll then split channel and buffer.

This change needs a lot of cleanups. At many locations, the parameter
or variable is still called "buf" which will become ambiguous. Also,
the "struct channel" is still defined in buffers.h.
diff --git a/include/types/buffers.h b/include/types/buffers.h
index ab56129..68b4319 100644
--- a/include/types/buffers.h
+++ b/include/types/buffers.h
@@ -27,7 +27,7 @@
 #include <types/stream_interface.h>
 
 /* The BF_* macros designate Buffer Flags, which may be ORed in the bit field
- * member 'flags' in struct buffer. Here we have several types of flags :
+ * member 'flags' in struct channel. Here we have several types of flags :
  *
  *   - pure status flags, reported by the lower layer, which must be cleared
  *     before doing further I/O :
@@ -174,7 +174,7 @@
 /* needed for a declaration below */
 struct session;
 
-struct buffer {
+struct channel {
 	unsigned int flags;             /* BF_* */
 	int rex;                        /* expiration date for a read, in ticks */
 	int wex;                        /* expiration date for a write or connect, in ticks */
@@ -187,7 +187,7 @@
 	unsigned int to_forward;        /* number of bytes to forward after out without a wake-up */
 	unsigned int analysers;         /* bit field indicating what to do on the buffer */
 	int analyse_exp;                /* expiration date for current analysers (if set) */
-	void (*hijacker)(struct session *, struct buffer *); /* alternative content producer */
+	void (*hijacker)(struct session *, struct channel *); /* alternative content producer */
 	unsigned char xfer_large;       /* number of consecutive large xfers */
 	unsigned char xfer_small;       /* number of consecutive small xfers */
 	unsigned long long total;       /* total data read */
diff --git a/include/types/proto_http.h b/include/types/proto_http.h
index 76c8e6b..158f094 100644
--- a/include/types/proto_http.h
+++ b/include/types/proto_http.h
@@ -305,7 +305,7 @@
 struct http_msg {
 	unsigned int msg_state;                /* where we are in the current message parsing */
 	unsigned int flags;                    /* flags describing the message (HTTP version, ...) */
-	struct buffer *buf;                    /* pointer to the buffer which holds the message */
+	struct channel *buf;                   /* pointer to the buffer which holds the message */
 	unsigned int next;                     /* pointer to next byte to parse, relative to buf->p */
 	unsigned int sov;                      /* current header: start of value */
 	unsigned int eoh;                      /* End Of Headers, relative to buffer */
diff --git a/include/types/session.h b/include/types/session.h
index a098002..9180a94 100644
--- a/include/types/session.h
+++ b/include/types/session.h
@@ -169,8 +169,8 @@
 	struct proxy *be;			/* the proxy this session depends on for the server side */
 	int flags;				/* some flags describing the session */
 	unsigned term_trace;			/* term trace: 4*8 bits indicating which part of the code closed */
-	struct buffer *req;			/* request buffer */
-	struct buffer *rep;			/* response buffer */
+	struct channel *req;			/* request buffer */
+	struct channel *rep;			/* response buffer */
 	struct stream_interface si[2];          /* client and server stream interfaces */
 	struct server *srv_conn;		/* session already has a slot on a server and is not in queue */
 	struct target target;			/* target to use for this session */
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index e181d57..1a75c8d 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -136,7 +136,7 @@
 	unsigned int state;     /* SI_ST* */
 	unsigned int prev_state;/* SI_ST*, copy of previous state */
 	unsigned int flags;     /* SI_FL_* */
-	struct buffer *ib, *ob; /* input and output buffers */
+	struct channel *ib, *ob; /* input and output buffers */
 	unsigned int exp;       /* wake up time for connect, queue, turn-around, ... */
 	void *owner;            /* generally a (struct task*) */
 	unsigned int err_type;  /* first error detected, one of SI_ET_* */