Added visual feedback on limits for sash-drag (Fix of previous broken behaviour: now unplits only if min pane size == 0 or if always-unsplittable style flag is used.) git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2552 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775