fix the following build error on octeon & ppc

In file included from ../../rak/priority_queue_default.h:41,
                 from ./../dht/dht_router.h:40,
                 from tracker_dht.cc:42:
../../rak/allocators.h: In static member function 'static T* rak::cacheline_allocator<T>::alloc_size(size_t)':
../../rak/allocators.h:109: error: 'uintptr_t' was not declared in this scope

--- a/rak/allocators.h
+++ b/rak/allocators.h
@@ -41,6 +41,7 @@
 
 #include <cstddef>
 #include <limits>
+#include <stdint.h>  /* for uintptr_t */
 #include <stdlib.h>
 #include <sys/types.h>