Added support for reading comments from a GIF image.

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

interface/wx/image.h

@@ -1136,6 +1136,12 @@ public:
             the resulting PNG file. Use this option if your application produces
             images with small size variation.
 
+        Options specific to wxGIFHandler:
+        @li @c wxIMAGE_OPTION_GIF_COMMENT: The comment text that is read from
+            or written to the GIF file. In an animated GIF each frame can have
+            its own comment. If there is only a comment in the first frame of
+            a GIF it will not be repeated in other frames.
+
         @param name
             The name of the option, case-insensitive.
         @return