Bug 62980: Make D* functions ignore case in headings

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1853268 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/ss/formula/functions/DStarRunner.java

 
     /**
      * For a given database returns the column number for a column heading.
+     * Comparison is case-insensitive.
      *
      * @param db Database.
      * @param name Column heading.
                 continue;
             }
             String columnName = OperandResolver.coerceValueToString(columnNameValueEval);
-            if(name.equals(columnName)) {
+            if(name.equalsIgnoreCase(columnName)) {
                 resultColumn = column;
                 break;
             }