Use 'executable' instead of 'exe' to configure name of tool chain tool
Start work on support for building native binaries targeted at different platforms

- Added 'targetPlatforms', a container of 'Platform' instances
- Create a binary for every target platform
- Include targetPlatform in the binaries variant dimensions
Verify the architecture of generated binary files
Added dumpbin based BinaryInfo for windows
Use Windows SDK 7.1 where available

- Verify existence of Windows SDK for Visual C++ tool chain based on install directory.
Create tasks for all defined tool chains, not just available ones

- Ensure that we always have at least one tool chain in the registry

better
Test for failure when building with unavailable tool chain
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