[USER32_APITEST] -Add a monster of a test to check if WM_DESTROYCLIPBOARD is blocking...

[USER32_APITEST] -Add a monster of a test to check if WM_DESTROYCLIPBOARD is blocking or not. Use a critical section while recording as we use a single message cache in two threads. After 50154, 50816, 50846 and 75616 changing back and forth, this test shows that 75616 is correct and making sure that it won't be changed again in the future, somehting that would break the ole clipboard.

svn path=/trunk/; revision=75663