cleanup library and some basic tests. Includes, add guards to includes
diff --git a/include/polarssl/havege.h b/include/polarssl/havege.h
index 1bad2b9..df26755 100644
--- a/include/polarssl/havege.h
+++ b/include/polarssl/havege.h
@@ -24,7 +24,7 @@
 #ifndef POLARSSL_HAVEGE_H
 #define POLARSSL_HAVEGE_H
 
-#include <string.h>
+#include <stddef.h>
 
 #define COLLECT_SIZE 1024