I tried to build some extensions with python 2.6 (built from sources
with VS 2008 express), and got some errors in the function
query_vcvarsall. The offending lines are:

if len(result) != len(interesting):
    raise ValueError(str(list(result.keys())))

I got a value error here. After some investigation, I realized that it
was because I did not install the SDK. I think the error message could
be isgnificantly improved if installing the SDK was suggested in the
exception message.