Chris Shoemaker's fixes to add custom columns to an Account view.

[David Hampton]

Log Message:
-----------
Chris Shoemaker's fixes to add custom columns to an Account
view.  Various cleanups and fixes for memory leaks.

Tags:
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gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/gnome:
        druid-hierarchy.c
    gnucash/src/gnome-utils:
        gnc-tree-model-account.c
        gnc-tree-view-account.c
        gnc-tree-view-account.h