REORG: include: move vars.h to haproxy/vars{,-t}.h

A few includes (sessions.h, stream.h, api-t.h) were added for arguments
that were first declared in function prototypes.
diff --git a/src/http_ana.c b/src/http_ana.c
index da16098..f7e5932 100644
--- a/src/http_ana.c
+++ b/src/http_ana.c
@@ -18,6 +18,7 @@
 #include <haproxy/htx.h>
 #include <haproxy/net_helper.h>
 #include <haproxy/regex.h>
+#include <haproxy/vars.h>
 #include <common/uri_auth.h>
 
 #include <haproxy/capture-t.h>
@@ -34,7 +35,6 @@
 #include <proto/stream.h>
 #include <proto/stream_interface.h>
 #include <proto/stats.h>
-#include <proto/vars.h>
 
 #define TRACE_SOURCE &trace_strm