Pushes other iterator onto this.
All calls performed on this are forwarded to other. If other returns
DONE, it is popped again and calls are handled by
this again.
This function is mainly used by objects implementing the iterator next function to recurse into substructures.
When resync is called on this, other
will automatically be popped.
MT safe.
| this |
The Iterator to use |
| other |
The Iterator to push |