Enhancements:
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* Implement "subspace selection" - so you can reduce a larger central set of variants to some smaller subset.  Fixes --python=X.Y on windows, with its zip_keys.  #2466
* Update cpan skeleton  #2156
* Pass through VSXY0COMNTOOLS env vars, so they're available in activate scripts called from outputs  #2453
* Add additional index-related files for Anaconda Navigator to use  #2463
* Add back CONDA_PY, CONDA_NPY, and friends, for backcompat with conda-build-all  #2469

Bug fixes:
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* Fix build_folder selection in dirty envs  #2445
* Fix an os.rename back to copy_into for cross-volume compatibility  #2451
* Clean up leftovers created by utils.get_recipe_abspath  #2459
* fix path globbing and filtering replacing prefix not at start of path, which broke file copying  #2468
* Don't recreate envs unnecessarily for recipes with no outputs section  #2470