Instead of forcing the tests to manually use memcmp(), specialize
CppUnit::assertion_traits<> for wxImage. This allows to simply use
CPPUNIT_ASSERT_EQUAL() and related macros with wxImage objects.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67616 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775