Create minetest_classic.xml

Tested on Chakra 2014.02 "Curie", Minetest Classic 1404.00
After some time of using minetest classic, this cleaner erased 23.3 MiB of debug logs
home page: http://minetest-classic.com/
Make lower case
add os="linux"
Merge pull request #35 from tiemay/patch-1

Create minetest_classic.xml