REORG: stconn: rename conn_stream.{c,h} to stconn.{c,h}

There's no more reason for keepin the code and definitions in conn_stream,
let's move all that to stconn. The alphabetical ordering of include files
was adjusted.
diff --git a/src/pool.c b/src/pool.c
index c82dbcb..973f8a0 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -19,13 +19,13 @@
 #include <haproxy/cfgparse.h>
 #include <haproxy/channel.h>
 #include <haproxy/cli.h>
-#include <haproxy/conn_stream.h>
 #include <haproxy/errors.h>
 #include <haproxy/global.h>
 #include <haproxy/list.h>
 #include <haproxy/pool.h>
 #include <haproxy/sc_strm.h>
 #include <haproxy/stats-t.h>
+#include <haproxy/stconn.h>
 #include <haproxy/thread.h>
 #include <haproxy/tools.h>