Set CONDA_NPY etc. to '' when they aren't set in config
Set CONDA_NPY etc. to '' when they aren't set in config

This fixes the recipe for conda build itself. Fixes #556.

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