MINOR: activity: report the number of failed pool/buffer allocations

Haproxy is designed to be able to continue to run even under very low
memory conditions. However this can sometimes have a serious impact on
performance that it hard to diagnose. Let's report counters of failed
pool and buffer allocations per thread in show activity.
diff --git a/include/types/activity.h b/include/types/activity.h
index 618785d..3725150 100644
--- a/include/types/activity.h
+++ b/include/types/activity.h
@@ -54,6 +54,8 @@
 	unsigned int accepted;     // accepted incoming connections
 	unsigned int accq_pushed;  // accept queue connections pushed
 	unsigned int accq_full;    // accept queue connection not pushed because full
+	unsigned int pool_fail;    // failed a pool allocation
+	unsigned int buf_wait;     // waited on a buffer allocation
 #if defined(DEBUG_DEV)
 	/* keep these ones at the end */
 	unsigned int ctr0;         // general purposee debug counter