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Update Makefile for AUTHORS renaming
Makefile: refuse to make dist in a dirty tree
Include COPYING etc in distributed zip file.
Makefile: add dist and clean targets
Makefile: fix quoting
You don't need to quote Makefile variables, and the quotes around
"$(FILES)" in the shell loop expanded it to:
""Readme.md extension.js metadata.json edit-groups""
So the two errors cancelled each other out.
Make sure edit-groups gets installed
Fully expunge references to stylesheet.css