updateFromXMLNode(): Connector/Socket updates can occur out of order

[chrisdembia]

XML versions 30508 and 30510 updated the XML format for connectors/sockets by implementing Component::updateFromXMLNode(). This code should be copied into base classes that had sockets before 30508/30510. The reason is made clear by what happened in #1577: update code for 30514 had to assume pre-30508 syntax because Joint doesn't have 30508 update code.

[chrisdembia]

Tom said in #1577:

Yeah, that was a source of confusion. I think the current design might be better than duplicating the code. Better still might be splitting up the code so that the model file is completely updated one version at a time. We might also then permit updates from an old version to a version that isn't current, which could help test backwards compatibility.

As a result, I am updating the name of this issue.

[chrisdembia]

Similar behavior could occur with other abstract classes that implement updateFromXMLNode, such as AbstractPathPoint (see #1595).

[tkuchida]

Potential issues caused by completely updating a derived class before Super::updateFromXMLNode() is called could be avoided if we complete the conversion from A to B before starting the conversion from B to C. We could do this by also passing the target version to updateFromXMLNode(). We would then be able to update to any desired version, which could also help test backwards compatibility with old models more rigorously. See #206.