[#1224] Equate Gentoo 2.1 to Ubuntu 12.04.

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Problem description
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paver.sh doesn't work on my Gentoo box.

Why we got into this (5 whys)
=============================

This is because paver.sh detects it as an unsupported Ubuntu version. 
This is because there will probably be no support for Gentoo.

Changes description
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This is a quick'n'dirty fix to equate any 2.1 LSB-aware distro as Ubuntu 12.04. Perhaps it will make sense in the future to differentiate between unsupported Ubuntu versions and other unsupported distributions.

How to try and test the changes
===============================

reviewers @adiroiban 

You may test this by making "lsb_release -sr" output 2.1.
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