Include cstddef in ots.h to fix compilation with gcc4.6

Patch from cmonde@gmail.com.



git-svn-id: http://ots.googlecode.com/svn/trunk@67 a4e77c2c-9104-11de-800e-5b313e0d2bf3
diff --git a/src/ots.h b/src/ots.h
index 5acb81f..09f3434 100644
--- a/src/ots.h
+++ b/src/ots.h
@@ -6,6 +6,7 @@
 #define OTS_H_
 
 #include <cstdarg>
+#include <cstddef>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>