CLEANUP: pool: only include pool-os from pool.c not pool.h
There's no need for the low-level pool functions to be known from all
callers anymore, they're only used by pool.c. Let's reduce the amount
of header files processed.
diff --git a/src/pool.c b/src/pool.c
index 48e51e6..ddea4c0 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -23,6 +23,7 @@
#include <haproxy/global.h>
#include <haproxy/list.h>
#include <haproxy/pool.h>
+#include <haproxy/pool-os.h>
#include <haproxy/sc_strm.h>
#include <haproxy/stats-t.h>
#include <haproxy/stconn.h>