CPaneContainerImpl improvements: Added PANECNT_DIVIDER to draw divider between title and pane, moved background drawing to OnEraseBackground to properly use transparent toolbar for close button, minor corrections for the close button size

git-svn-id: http://svn.code.sf.net/p/wtl/code/trunk/wtl@598 4beafcb9-bf40-0410-b8f5-b741cf90ec0e