Lua environment variables and supporting parallel versions

[John Belmonte <john@...>]

For Lua packagers: I realized that to support multiple installed
versions of Lua, versioned aliases of the Lua environment variables
(LUA_INIT, LUA_PATH, and LUA_CPATH) are needed.  I propose names as
follows (e.g. for Lua 5.1):

  LUA_5_1_INIT
  LUA_5_1_PATH
  LUA_5_1_CPATH

If a versioned alias is set, it takes precedence over the non-versioned
variable.

--John