message: Fix unintentional exclusion of code
  consolidate_free_read_only() was hidden behind REALM_ALLOC_DEBUG flag.
diff: @@ -356,7 +356,9 @@ ref_type GroupWriter::write_group()
  m_free_versions.copy_on_write(); // Throws
  #if REALM_ALLOC_DEBUG
  std::cout << " In-mem freelist before consolidation: " << m_group.m_alloc.m_free_read_only.size();
  +#endif
  m_group.m_alloc.consolidate_free_read_only(); // Throws
  +#if REALM_ALLOC_DEBUG
  std::cout << " In-mem freelist after consolidation: " << m_group.m_alloc.m_free_read_only.size() << std::endl;
  #endif
  const SlabAlloc::chunks& new_free_space = m_group.m_alloc.get_free_read_only(); // Throws
  