add --retry 5 to curl opts in install_db4.sh

contrib/install_db4.sh

@@ -51,7 +51,7 @@ http_get() {
   if [ -f "${2}" ]; then
     echo "File ${2} already exists; not downloading again"
   elif check_exists curl; then
-    curl --insecure "${1}" -o "${2}"
+    curl --insecure --retry 5 "${1}" -o "${2}"
   else
     wget --no-check-certificate "${1}" -O "${2}"
   fi