build: Fixing gcc 4.8.1 warnings from KeyLocator

Change-Id: I89910f3623e0c903246cc4931343fb6f20bd72f3
diff --git a/src/key-locator.hpp b/src/key-locator.hpp
index 65a966b..dcae6bf 100644
--- a/src/key-locator.hpp
+++ b/src/key-locator.hpp
@@ -18,7 +18,7 @@
   struct Error : public std::runtime_error { Error(const std::string &what) : std::runtime_error(what) {} };
   
   enum {
-    KeyLocator_None = 4294967295,
+    KeyLocator_None = 65535, // just an arbitrarily large number (used only internally)
     KeyLocator_Name = 0,
     
     KeyLocator_Unknown = 255