[#2123] AIX dev buildslave setup.

Why?
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Because we need an AIX dev buildslave.


Solution?
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Update the AIX bits in `chevah-os-bootstrap`.


How to check?
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Please review changes.
On a freshly installed AIX 5.3+ machine execute the `bootstrap.sh` script as root.
Log in as the newly created user `chevah` and execute `git.sh` to get git working.
Clone HTTP/HTPPS repos, eg. . http://git.chevah.com/python-package.git and https://github.com/chevah/python-package.git

reviewers: @adiroiban
Why not add the extra space in the initial bootstrap script?

I prefer to keep this script to the core basic so that we can share it with other people trying to compile git on AIX.