Fix for the bug #4014 (prepared SELECT in embedded server)

Problem is that store_string_aux calls 'wrong' net_store_data


sql/protocol.h:
  I tried not to do net_store_data virtual - it's going to work a bit slower -
  using the fact that Protocol_simple and Protocol_prep have different
  implementation for 'store' methods.
  But now the store_string_aux method works for both.
  Well we still can try to make separate versions for Protocol_prep and
  Protocol_simple, but i prefer to make net_store_data virtual for
  embedded server so we won't have similar problems in the future

sql/protocol.h

@@ -35,8 +35,10 @@ class Protocol
   enum enum_field_types *field_types;
 #endif
   uint field_count;
+#ifndef EMBEDDED_LIBRARY
   bool net_store_data(const char *from, uint length);
-#ifdef EMBEDDED_LIBRARY
+#else
+  virtual bool net_store_data(const char *from, uint length);
   char **next_field;
   MYSQL_FIELD *next_mysql_field;
   MEM_ROOT *alloc;