Add check nil var with bug from crash server.
fixes #438

Saves on bandwidth, however the code is still accessible via the formspec.

If LuaControllers handle sensitive information, hacked clients could get this information from the LuaController. Marking the memory as private fixes this and saves a small amount of bandwidth.

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It was moved a long time ago and the former is not guaranteed to be available.
fixes #424

Because of working inside the sandbox, it was unable to print tables.

Also, fix globals assignment.

* Let things fall behind movestones

Add missing sound effects and fix wrong pressure plate sounds

- 'setting_get' with 'settings:get'
- 'setting_getbool' with 'settings:get_bool'

Fixed method name to get the position.

Fixes:
1. Lack of 'safe' on minetest.deserialize usage
2. String sandbox bypass via (""):evil()
3. Loss of upcoming digilines messages on server shutdown
4. LCs failing to show information on some errors
5. Interrupt IDs as infinite data storage

Register both luacontroller and microcontroller variations of detector craft recipes.

* Close vulnerability and optimize digiline_send

`digiline_send` as it previously existed was vulnerable to a
time-of-check-to-time-of-use vulnerability in which a table could be
sent, size-checked, and then modified after the send but before
delivery. This would allow larger tables to be sent. It was also slow
because it called `minetest.serialize`. Fix both of these by
implementing custom message cleanup logic which simultaneously computes
the message’s cost.

* Clean up interaction with Digilines

Use `minetest.global_exists` to avoid an undefined global variable
warning when operating a Luacontroller with Digilines not available. Use
the new `digilines` table in preference to the old `digiline` table.

* Copy received messages

When a Digiline message is received at a Luacontroller, copy it so that
local modifications made by the Luacontroller code will not modify
copies of the table that are being passed to other nodes on the Digiline
network.