Parent related problems in Helma 1.6.0

• Not possible to define collections of mountpoints in _parent because it only accepts a two element path
• Helma does quite a bit of guesswork to determine the child-parent relationship in methods like Node.add* and Node.set*. This is the cause for bug 543.
• There are some places where helma doesn't distinguish between embedded and relational db. One example is bug 554, which is caused by Helma marking clean or deleted nodes as modified before adding them to a subnode relation.

Possible solutions - we need to decide whether the target is Helma 1.6.1 or 1.7.0:

• Add third segment to _parent info for collections of mountpoints
• Add optional getParentElement() callback that works similar to getChildElement()

• Either remove the parent guessing code, or limit it to cases where no _parent has been specified.
• Do not mark nodes as modified because they're added to a transient node.