[isabelle-dev] PLATFORMS: Linux base-line is Ubuntu 12.04 LTS

[Makarius]

See also
http://isabelle.in.tum.de/repos/isabelle/file/2803d2b8f85d/Admin/PLATFORMS#l33

Former Ubuntu 10.04 LTS has become a bit old, and is no longer
maintained by Canonical. 12.04 remains officially active until 04/2017.


The Mac OS X baseline is still 10.8 (Mountain Lion), which is also from
2012. Lets see if we can keep this window into the past open, despite
the very few Apple testing machines in the background.


	Makarius