Seems to be a typo. In setIdleLimit the limit value is a ssize_t.
Newer versions of gcc do not complain about this but OpenBSD's gcc does.

--- src/mem.cc.orig	Wed Jun  2 12:10:25 2010
+++ src/mem.cc	Wed Jun  2 12:10:41 2010
@@ -346,7 +346,7 @@
 void
 memConfigure(void)
 {
-    size_t new_pool_limit;
+    ssize_t new_pool_limit;
 
     /** Set to configured value first */
     if (!Config.onoff.mem_pools)