[8u] Review request: RT-23245: TreeView moves its origin position if the root item has a parent

[Jonathan Giles]

David, Kevin, Steve,

Could you please review the following:

https://javafx-jira.kenai.com/browse/RT-23245
https://javafx-jira.kenai.com/secure/attachment/42016/rt23245.patch

Note: there is a proposed method deprecation, but it isn't critical to
the fix.

Thanks,
-- Jonathan