Utilize the new object tracking functions in these gnucash base class

[David Hampton]

Log Message:
-----------
Utilize the new object tracking functions in these gnucash base class
objects.

Tags:
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gnucash-gnome2-dev

Modified Files:
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    gnucash/src/gnome-utils:
        gnc-plugin-page.c
        gnc-plugin.c
        gnc-tree-view.c
        gnc-tree-view.h