Adding cmake module to find various bits of the DirectX SDK from Microsoft

File originally obtained from game kit @ https://gamekit.googlecode.com/svn-history/r841/trunk/CMake/Packages/FindDirectX.cmake
Makes building the DirectX 9 sample optional, auto detects if it should be built only if DirectX is installed.
Removes the linking of DirectX libraries to all samples which do not require it.
Fixed directs examples to only build in Windows
Better detection of DirectX 9 in environments like VisualStudio where the IDE installation may include some parts of DirectX but not the bits we require.
Merge pull request #162 from dwimsey/feature/optional-build-directx-samples

Feature/optional build directx samples