MEDIUM: servers: Add a command to limit the number of idling connections.

Add a new command, "pool-max-conn" that sets the maximum number of connections
waiting in the orphan idling connections list (as activated with idle-timeout).
Using "-1" means unlimited. Using pools is now dependant on this.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 9fca4bd..5b24fcf 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -11972,6 +11972,14 @@
 
   Actions are disabled by default
 
+pool-max-conn <max>
+  Set the maximum number of idling connections for a server. -1 means unlimited
+  connections, 0 means no idle connections. The default is -1. When idle
+  connections are enabled, orphaned idle connections which do not belong to any
+  client session anymore are moved to a dedicated pool so that they remain
+  usable by future clients. This only applies to connections that can be shared
+  according to the same principles as those applying to "http-reuse".
+
 port <port>
   Using the "port" parameter, it becomes possible to use a different port to
   send health-checks. On some servers, it may be desirable to dedicate a port