Build 4.5.0.12 of xlsgen improves the speed of calculations by 25%

Work has been done in two scenarios : cell traversal (i.e. calculations with many depending cells carrying little or no formulas) ; and deep nesting (i.e. calculations with formulas depending on a chain of other formulas). That's 25% faster. And that includes 10% less memory page faults for the former scenario.