Add unit test for Clipboard>>availableFormats
Add unit test for Clipboard>>availableFormats

Regression test for #873

jgfoster/Dolphin,objectarts/Dolphin,dolphinsmalltalk/Dolphin,shoshanatech/Dolphin,jgfoster/Dolphin,shoshanatech/Dolphin,dolphinsmalltalk/Dolphin,shoshanatech/Dolphin,jgfoster/Dolphin,objectarts/Dolphin,jgfoster/Dolphin,dolphinsmalltalk/Dolphin,shoshanatech/Dolphin,dolphinsmalltalk/Dolphin