172 SoFieldContainer and private fields

    TGS has support for private fields, Coin doesn't.
    Something like this:

#define SO_NODE_ADD_PRIVATEFIELD(fieldname, defvalue) \
{ \
  classMutex->writelock(); \
  SO__NODE_CHECK_CONSTRUCT(__FILE__); \
  if ( firstInstance ) \
    fieldData->addField(this, SO__QUOTE(fieldName), &this->fieldName); \
  this->fieldName.setValue(defValue); \
  this->fieldName.setContainer(this); \
  this->fieldName.setFieldType(0); \
  classMutix->writeunlock(); \
}

    20041116 larsa.
