This makes a number of changes:
  * Remove the dependency on marshal by using string.dump and loadstring.
  * Use lua_tolstring rather than having Lua functions pass string lengths to C++.
  * Move lua_api/l_async_events.* to cpp_api/s_async.*, where it belongs.
  * Make AsyncWorkerThread a child of ScriptApiBase, this removes some duplicate functionality.
  * Don't wait for async threads to shut down.  (Is this safe?  Might result in corruption if the thread is writing to a file.)
  * Pop more unused items from the stack
  * Code style fixes
  * Other misc changes

This reverts commit 5b518ed2.

This caused duplicate tracebacks and tracebacks when unwanted.
It also ignored the level argument to error() and didn't pass the message (or level) to debug.traceback().
Use xpcall() or lua_pcall()'s errorhandler argument instead.

since the object is not immediately removed, any other code may still
think an object is there, therefore leading to item duplication. This code
therefore sets the itemstring to '' after the object is picked up to avoid
such issues

Parallax mapping with slope information.
Overriding normal maps.

As suggested by qwrwed.

Fixed lua error when none of the worlds or servers selected are and connect,
delete or configure buttons used.

This reverts commit 4e5760a5.

Similar to assuming a selection box for the nodebox drawtype, minetest.register_item() now assumes a selection box for the fencelike drawtype.