Fix a bunch of warnings generated by doxygen.

[David Hampton]

Log Message:
-----------
Fix a bunch of warnings generated by doxygen.

Tags:
----
gnucash-gnome2-dev

Modified Files:
--------------
    gnucash:
        ChangeLog
    gnucash/src/backend/file:
        io-gncxml-v2.h
    gnucash/src/business/business-gnome:
        gnc-plugin-page-invoice.h
    gnucash/src/core-utils:
        gnc-gconf-utils.h
    gnucash/src/engine:
        SchedXaction.h
        TransLog.h
        Transaction.h
        gnc-commodity.h
        gnc-pricedb.c
        qofbackend-p.h
    gnucash/src/gnome:
        dialog-sx-from-trans.c
        druid-merge.h
        druid-stock-split.c
        gnc-plugin-page-register.h
        gnc-split-reg.c
        window-main-summarybar.c
    gnucash/src/gnome-utils:
        dialog-account.h
        dialog-commodity.c
        dialog-preferences.c
        dialog-preferences.h
        druid-gconf-setup.c
        druid-gconf-setup.h
        gnc-date-edit.h
        gnc-dense-cal.c
        gnc-embedded-window.h
        gnc-gnome-utils.h
        gnc-main-window.c
        gnc-main-window.h
        gnc-plugin-manager.h
        gnc-plugin-menu-additions.c
        gnc-plugin-page.c
        gnc-plugin-page.h
        gnc-plugin.c
        gnc-tree-model-commodity.h
        gnc-tree-model-price.h
        gnc-tree-view-account.h
        gnc-tree-view-commodity.h
        gnc-tree-view-price.h
        gnc-tree-view.c
        print-session.h
    gnucash/src/import-export:
        import-settings.h
    gnucash/src/register/register-core:
        combocell.h