Fixed #10. Use AssemblyInformationalVersion.
This commit fixes issue #10, "Use AssemblyInformationalVersion when present."  Care was taken to ensure that, when determining the referenced assembly's ProductVersion, FileVersion, or AssemblyVersion, the assembly was not loaded into MSBuild's AppDomain and therefore locking the assembly.
Merge pull request #11 from robv8r/robv8r-10-versioning

Fixed #10. Use AssemblyInformationalVersion.