Ppu

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* Fix rm.py: do not ask to remove read-only files when -f is active.

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* rm.py ask interactively to remove read-only files or directories.

* Add options -s --silent --quiet for cmp.py.

* Add option -f for rm.py.

* PyPy.

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* Add option -r for rm.py.

* Use remove-old-files.py to cleanup pip cache.

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* Add package 'ppu'.

* Add module ppu/find_executable.py.

* Add script which.py.

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* Convert README to reST.

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* Fix release: build scripts with '/usr/bin/env python'