Make PERL_CORE check more lenient (any version means its not added to requirements), and prevent duplicates with --recursive.
Make PERL_CORE check more lenient (any version means its not added to requirements), and prevent duplicates with --recursive.

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