fix async problem when scrolling to a row that is no longer available
performance fix for selection rendering; exit codes in getCell method
scrollbar modes: scrollH, scrollV = scroll | auto | none
make sure scrollbars are shown/hidden in auto mode
make sure scroll dimensions are not taken into account when scroll is hidden
stretchH strategies: all and last
fix tests in IE8
make all tests pass in IE8-9, FF, Ch (still problems in IE7 and O)
auto width should take into account if scrollbar is visible
new options currentRowClassName & currentColumnClassName
don't show sliders in top left corner during initialization
microoptimizations in isCellVisible
cleanup: remove references to rowHeader function that was not used
(frozenColumns is used instead)
breaking change: columnHeaders now receives TH node as second argument and is supposed to render column header there
do not throw Error because it affects async rendering after Handsontable was destroyed