Lua 5.2 boostrapping compatibility

Hey,

I just rewrote my changes to enable boostrapping with Lua 5.2 but keeping the code compatible with lua 5.1, so that luadist-git can be installed with both versions.

So no need for a lua-5.2 branch ;-)

Best regards,

  Cyril

PS : as noted previously :
 - one need to checkout the luasocket "unstable" branch to compile luasocket with Lua 5.2.
 - LuaDist is built with Lua5.2, i.e. the _boostrap creation is OK and includes Lua5.2, but for a reason I ignore when LuaDist builds with LuaDist it actually (re)checkouts and builds Lua5.1.5 and fills the _install directory with that version instead of Lua5.2. Any idea why ?