BUG/MINOR: stats:Fix incorrect printf type.

The value is defined in include/types/global.h to be an unsigned int.
The type format in the printf is for a signed int. This eventually wraps
around.

WT: This bug was introduced in 1.5.
(cherry picked from commit b197d7f433fc126f754df3923761d2dcc0893f69)
diff --git a/src/dumpstats.c b/src/dumpstats.c
index 1070ff4..b616478 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -2492,7 +2492,7 @@
 	             "Hard_maxconn: %d\n"
 	             "CurrConns: %d\n"
 		     "CumConns: %d\n"
-		     "CumReq: %d\n"
+		     "CumReq: %u\n"
 #ifdef USE_OPENSSL
 		     "MaxSslConns: %d\n"
 	             "CurrSslConns: %d\n"