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/flt_spoe.c b/src/flt_spoe.c
index 010dac2..6acb9f4 100644
--- a/src/flt_spoe.c
+++ b/src/flt_spoe.c
@@ -21,6 +21,7 @@
 #include <haproxy/thread.h>
 #include <haproxy/pool.h>
 #include <haproxy/time.h>
+#include <haproxy/vars.h>
 
 #include <haproxy/arg-t.h>
 #include <types/global.h>
@@ -41,7 +42,6 @@
 #include <proto/stream_interface.h>
 #include <proto/task.h>
 #include <proto/tcp_rules.h>
-#include <proto/vars.h>
 
 #if defined(DEBUG_SPOE) || defined(DEBUG_FULL)
 #define SPOE_PRINTF(x...) fprintf(x)