d3dx8: Dynamically import d3dx8 in the tests so the tests can be skipped if the dll is not found

[Paul Vriens]

Maarten Lankhorst wrote:
> This is better then downright crashing on the missing dlls.
> 
> This patch was created using grep and sed. :-)
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Hi Maarten,

When do you see a crash? Winetest itself already checks if a dll is present. If 
it's not, the tests are skipped as can be seen on test.winehq.org..

-- 
Cheers,

Paul.