Adds support for the environment variable _

http://istasi.dk/printenv.png yes, this clearly editted, due to my heighten paranoid level

src/main/resources/assets/opencomputers/loot/OpenOS/bin/sh.lua

@@ -118,7 +118,9 @@ local function execute(env, command, ...)
   local thread, reason = process.load(shell.resolve(program, "lua"), env, nil, command)
   if not thread then
     return false, reason
-  end
+  else
+    os.setenv ( '_', shell.resolve (program, "lua") )
+  end 
   local result = nil
   -- Emulate CC behavior by making yields a filtered event.pull()
   while args[1] and coroutine.status(thread) ~= "dead" do
@@ -189,4 +191,4 @@ else
     error(result[2], 0)
   end
   return table.unpack(result, 2)
-end
+end