Enhancements:
-------------

* use symlinks when copying files from files sources to improve performance  #1867

Bug fixes:
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* reset build folder for each built package (fixes building multiple recipes in one command)  #1842
* wrap copy of test/source_files so that errors don't prevent a successful build  #1843
* Restore permissions when extracting from zipfiles  #1855
* pass through several Windows-specific environment variables  #1859, #1862
* python 2 os.environ string type compatibility fix  #1861
* fix indentation breaking perl package testing  #1872
* reduce scope of git try/except block so that GIT_FULL_HASH is available even if tags are not.  #1873
* fix license family comparison, especially for public-domain  #1875
* Remove python header being added to all run_test.* files  #1876