MINOR: config: report the number of processes using a peers section in the error case

It can be helpful to know how many different processes try to use the
same peers section when trying to find the culprits.
(cherry picked from commit 64c5722e051768188754bd4c25a440ecd9103b38)
diff --git a/src/cfgparse.c b/src/cfgparse.c
index ede7681..d78a23c 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -7425,9 +7425,9 @@
 				/* either it's totally stopped or too much used */
 				if (curpeers->peers_fe->bind_proc) {
 					Alert("Peers section '%s': peers referenced by sections "
-					      "running in different processes. Check global.nbproc"
-					      " and all tables' bind-process settings.\n",
-					      curpeers->id);
+					      "running in different processes (%d different ones). "
+					      "Check global.nbproc and all tables' bind-process "
+					      "settings.\n", curpeers->id, popcount(curpeers->peers_fe->bind_proc));
 					cfgerr++;
 				}
 				stop_proxy(curpeers->peers_fe);