See #337 for details.

New overheating system that doesn’t use the meta.

* Support detection of multiple players in object detector
* Add distance parameter to node detector
* Fix area protection

* Fix inconsistent insulated mesecon names
* Clarify lightstone names
* Rename meselamp to "Mesecon Lamp"
* Use capitalization "Luacontroller" consistently
* Cleanup / improvements for logic gate naming

It used to be so that you could gain two sticky movestones out of one normal one,
this didn't make much sense.

Fixes #289

Make "on" water turbine animated!

This uses a fairly simple trick: the textures are animated, while the
model is static and has a number of rotated copies of the parts that are
seen to move (four copies of the blades, eight copies of the top/bottom
and their edges).  The opaque parts of the textures then decide which of
those faces' copies are visible in each frame.

This allows finding all of them by searching
"insulated" in the creative menu.

caused by an oversight in ececf525

This removes the weird "holes" in the isolation of the crossing

Buttons and levers can now also be pointed upwards / downwards which will make them connect to corresponding up / down receivers. You will need to use the screwdriver for this.

Receivers cannot be rotated using the screwdriver anymore.

This also makes turbines compatible with any liquid that is in the `water` group and has `liquidtype == "flowing"`.

Thanks to @ShadowNinja for reporting this
Make sure functions that are keys in tables and functions inside nested tables also get removed when using digiline_send.

Restrict maximum length of messages to 50.000 characters and disable sending functions or table references over the wire. Restrict types of channel variable to string, number or boolean.

The missing length restriction made DoS-like attacks possible by overflowing memory using string concatenation. Thanks to gamemanj for disclosing this issue.

There is no more need for that since VoxelManip caching makes sure we
always get an answer to get_node_force.

Duplicating that small piece of code seems like a better idea than
putting the undo-forceloading code back into util.lua. This way, it is
easier to remember to remove that unneccesary code after a couple of
months / years, when people have transitioned. This also means we can
make changes to the code in util.lua without breaking old code.

The change that required this compatibility layer happened in
2014, so other mods have had a lot of time to update.

Instead of seperately looking for onstate receptors along equipotential
sections of the circuit before turning off, do that while already
modifying the VoxelManip. In case an onstate receptor is found, discard
the VoxelManip cache, otherwise commit it after turnoff is completed.

It is no longer possible for get_node_force to return nil if the target
location does, in fact, exist, because a VM will always be able to load
it (whereas a forceload might not, due to exhaustion of forceload
resources). So it is no longer necessary to handle get_node_force
returning nil by deferring processing.