Tested on GTK2, MSW and Mac.
Adapted various generic dialogs to stretch the
button sizer so that the buttons don't end
up centered but right aligned.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31198 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775