[#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
Actually I was thinking the other way around, that I should remove the lines adding 3GB to /home in the bootstrap script because that is what we need on our machines, not something of general interest. What do you think? 

While when compiling curl and git, the added space is a requirement and thus needed no matter what. And I think this should be clear in the script. If it's not I'll try to make the comments more clear.