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/proto/proto_http.h b/include/proto/proto_http.h
index 06fe292..69d932c 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -66,27 +66,27 @@
 int process_cli(struct session *t);
 int process_srv_data(struct session *t);
 int process_srv_conn(struct session *t);
-int http_wait_for_request(struct session *s, struct buffer *req, int an_bit);
-int http_process_req_common(struct session *s, struct buffer *req, int an_bit, struct proxy *px);
-int http_process_request(struct session *t, struct buffer *req, int an_bit);
-int http_process_tarpit(struct session *s, struct buffer *req, int an_bit);
-int http_process_request_body(struct session *s, struct buffer *req, int an_bit);
+int http_wait_for_request(struct session *s, struct channel *req, int an_bit);
+int http_process_req_common(struct session *s, struct channel *req, int an_bit, struct proxy *px);
+int http_process_request(struct session *t, struct channel *req, int an_bit);
+int http_process_tarpit(struct session *s, struct channel *req, int an_bit);
+int http_process_request_body(struct session *s, struct channel *req, int an_bit);
 int http_send_name_header(struct http_txn *txn, struct proxy* be, const char* svr_name);
-int http_wait_for_response(struct session *s, struct buffer *rep, int an_bit);
-int http_process_res_common(struct session *t, struct buffer *rep, int an_bit, struct proxy *px);
-int http_request_forward_body(struct session *s, struct buffer *req, int an_bit);
-int http_response_forward_body(struct session *s, struct buffer *res, int an_bit);
+int http_wait_for_response(struct session *s, struct channel *rep, int an_bit);
+int http_process_res_common(struct session *t, struct channel *rep, int an_bit, struct proxy *px);
+int http_request_forward_body(struct session *s, struct channel *req, int an_bit);
+int http_response_forward_body(struct session *s, struct channel *res, int an_bit);
 
 void debug_hdr(const char *dir, struct session *t, const char *start, const char *end);
 void get_srv_from_appsession(struct session *t, const char *begin, int len);
-int apply_filter_to_req_headers(struct session *t, struct buffer *req, struct hdr_exp *exp);
-int apply_filter_to_req_line(struct session *t, struct buffer *req, struct hdr_exp *exp);
-int apply_filters_to_request(struct session *s, struct buffer *req, struct proxy *px);
-int apply_filters_to_response(struct session *t, struct buffer *rtr, struct proxy *px);
+int apply_filter_to_req_headers(struct session *t, struct channel *req, struct hdr_exp *exp);
+int apply_filter_to_req_line(struct session *t, struct channel *req, struct hdr_exp *exp);
+int apply_filters_to_request(struct session *s, struct channel *req, struct proxy *px);
+int apply_filters_to_response(struct session *t, struct channel *rtr, struct proxy *px);
 void manage_client_side_appsession(struct session *t, const char *buf, int len);
-void manage_client_side_cookies(struct session *t, struct buffer *req);
-void manage_server_side_cookies(struct session *t, struct buffer *rtr);
-void check_response_for_cacheability(struct session *t, struct buffer *rtr);
+void manage_client_side_cookies(struct session *t, struct channel *req);
+void manage_server_side_cookies(struct session *t, struct channel *rtr);
+void check_response_for_cacheability(struct session *t, struct channel *rtr);
 int stats_check_uri(struct stream_interface *si, struct http_txn *txn, struct proxy *backend);
 void init_proto_http();
 int http_find_header2(const char *name, int len,