use POILogger
Fix Bug 53446 - Fixed some problems extracting PNGs. (Only HSSF)
(sync from poi)
fixed bug 53432
fixed bug 53588
Bug 53974 - Avoid exception when constructing HSSFWorbook on Google App Engine
Bug 53763: avoid style mess when using HSSFOptimiser
Bug 53404 - Fixed compatibility issue with modifying xls files created by POI-3.6 and earlier
HSSFOptimiser
HSSFOptimiser will now also tidy away un-used cell styles, in addition to duplicate styles(poi-developers)