Applied (modified) patch by troelsk. Changed comments (which are allowed per frame in an animated GIF) to be read using wxIMAGE_OPTION_GIF_COMMENT with wxImage.GetOption. Added unit tests for reading and writing GIF comments. Closes #12843. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66828 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775