skeleton pypi: fail better for packages with bad urls
skeleton pypi: fail better for packages with bad urls

Fixes #367.

mwcraig/conda-build,frol/conda-build,shastings517/conda-build,shastings517/conda-build,mwcraig/conda-build,mwcraig/conda-build,dan-blanchard/conda-build,sandhujasmine/conda-build,shastings517/conda-build,ilastik/conda-build,rmcgibbo/conda-build,sandhujasmine/conda-build,sandhujasmine/conda-build,dan-blanchard/conda-build,frol/conda-build,ilastik/conda-build,rmcgibbo/conda-build,frol/conda-build,rmcgibbo/conda-build,dan-blanchard/conda-build,ilastik/conda-build