[#1847] Move os setup to compat and update to latest paver script.


Problem description
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This is a maintenance branch which support a few changes in chevah.compat package.



Changes description
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Import latest paver.sh script which implements independent repository.

setup_os and teardown_os were moved to compat as when developing that code all code changes are in compat, and the development is simplified.

nose_runner will call sys.exitfunc since we don't use sys.exit() so we try to mitigate this. This was required for calling atexit functions.

atexit is neede to support PAM on aix https://github.com/chevah/python-pam/compare/aix-arpy


How to try and test the changes
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reviewers @alibotean 

Check that changes make sense.