Audit use of gnc_numeric rounding and denom specification.

[Linas Vepstas]

Log Message:
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Audit use of gnc_numeric rounding and denom specification.
Change GNC_RND to GNC_HOW_RND

Modified Files:
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    gnucash/src/engine:
        Account.c
        Scrub.c
        Scrub3.c
        Transaction.c
        engine-helpers.c
        qofquerycore.c