MEDIUM: log: use log_format for mode tcplog

Merge http_sess_log() and tcp_sess_log() to sess_log() and move it to
log.c

A new field in logformat_type define if you can use a logformat
variable in TCP or HTTP mode.

doc: log-format in tcp mode

Note that due to the way log buffer allocation currently works, trying to
log an HTTP request without "option httplog" is still not possible. This
will change in the near future.
diff --git a/include/proto/log.h b/include/proto/log.h
index 34d3813..66fbe34 100644
--- a/include/proto/log.h
+++ b/include/proto/log.h
@@ -35,9 +35,17 @@
 extern struct pool_head *pool2_requri;
 
 extern char *log_format;
+extern char default_tcp_log_format[];
 extern char default_http_log_format[];
 extern char clf_http_log_format[];
 
+
+/*
+ * send a log for the session when we have enough info about it.
+ * Will not log if the frontend has no log defined.
+ */
+void sess_log(struct session *s);
+
 /*
  * Parse args in a logformat_var
  */
@@ -98,10 +106,6 @@
  */
 
 void __send_log(struct proxy *p, int level, char *message, size_t size);
-/*
- * send a log for the session when we have enough info about it
- */
-void tcp_sess_log(struct session *s);
 
 /*
  * returns log level for <lev> or -1 if not found.