Test that media constructors behave consistently.

TEST(audioJS instanceof HTMLAudioElement) OK
TEST(audioJS instanceof HTMLMediaElement) OK
TEST(!(audioJS instanceof HTMLVideoElement)) OK
TEST(audioElem instanceof HTMLAudioElement) OK
TEST(audioElem instanceof HTMLMediaElement) OK
TEST(!(audioElem instanceof HTMLVideoElement)) OK
TEST(videoElem instanceof HTMLVideoElement) OK
TEST(videoElem instanceof HTMLMediaElement) OK
TEST(!(videoElem instanceof HTMLAudioElement)) OK
END OF TEST