Feature Request: addMergedRegionUnsafe on rowspan/colspan

[miao1007]

The default implication of rowspan is addMergedRegion and it's really magic.

However the method addMergedRegion is slow on large data because it need to check range at every loop, see detail at http://apache-poi.1045710.n5.nabble.com/Bug-60397-New-very-slow-Cell-Merge-for-SXSSFWorkbook-td5725704.html

give a choice on if use the unsafe merge would be more helpful.

public interface CellDefinition extends HasStyle {

+    CellDefinition colspanUnsafe(int span);
+    CellDefinition rowspanUnsafe(int span);

}

[musketyr]

I'm sorry I haven't answered yet! It thought I've already had. I'll take a look as soon as possible.