Bug 797390 - xaccAccountRecomputeBalance also tallies no-closing balances

Add a few API, enough for fixing bug 797326 easily.

libgnucash/engine/SplitP.h

@@ -123,6 +123,7 @@ struct split_s
      * These balances apply to a sorting order by date posted
      * (not by date entered). */
     gnc_numeric  balance;
+    gnc_numeric  noclosing_balance;
     gnc_numeric  cleared_balance;
     gnc_numeric  reconciled_balance;
 };