No changes, just add another case to a switch on wxMouseButton.

Fix warnings given when wx headers are compiled with g++ -Wswitch-enum option.

Also make the assert messages more precise and less verbose as there is no
need to include the function name in them, all relatively recent compilers
provide it via __FUNCTION__ and wxFAIL_MSG() already uses it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69756 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775