Patch from Chris Shoemaker to remove unneeded header files.

[David Hampton]

Log Message:
-----------
Patch from Chris Shoemaker to remove unneeded header files. Add a few
comments.

Tags:
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gnucash-gnome2-dev

Modified Files:
--------------
    gnucash/src/app-utils:
        gnc-euro.c
        gnc-ui-util.h
    gnucash/src/gnome-utils:
        dialog-commodity.h
        gnc-currency-edit.c