Merge pull request #18 from pbhogan/master

#undef DEBUG for compatibility with environments that define DEBUG (like Xcode)

include/mruby.h

@@ -388,6 +388,10 @@ void mrb_write_barrier(mrb_state *, struct RBasic*);
 
 #define MRUBY_VERSION "Rite"
 
+#ifdef DEBUG
+#undef DEBUG
+#endif
+
 #if 0
 #define DEBUG(x) x
 #else