File/dir dialog styles and other changes (patch 1488371):

File/dir dialog styles and other changes (patch 1488371):

- check invalid combinations of styles in wxFileDialogBase::Create()
- use wxFD_XXX naming convention for wxFileDialog styles
- replaces wxDD_NEW_DIR_BUTTON with wxDD_DIR_MUST_EXIST
- removes #ifdef __WXGTK24__ / #endif blocks from wxGTK code
- removes wxFileDialogBase::Get/SetStyle and wxFileDialogBase::m_fileName
- renames wxDirDialogGTK to wxDirDialog

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39402 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775