Doc updates, wxsizer et al

 Doc updates, wxsizer et al
 wxFileDialog displays current dir now,
 wxTipProvider uses statictext for headline
 messagebox (and other) dialogs now always display
   an OK buttons, unless wxYES_NO is given
 Appending a menu to a menu bar after having called
   wxFrame::SetMenuBar() should now work
 Added test to configure so that it correctly sets
  compiler flags etc if GCC is used on Solaris and
  IRIX instead of CC, also changed default shared
  library create to GCC from G++ on some platforms
  (as previously already Linux)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@3429 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775