* Deprecate non-string IIDs
* Restrict tabular IIDs to proper trees
Fixes crash on recursive interrupt ID (#473)

* Add insulated double corner
* Make single corner curved to match double corner
* Remove obsolete regular corner textures

Allow admins (i.e. players with the `protection_bypass` privilege) digging any command block

The handles were never used anyway

Reduce actionqueue complexity, thus faster execution
Improve code style
Add documentation/explanations

mesecons.tablecopy didn’t support recursive tables, while Minetest table.copy works well for them.

Recompress losslessly using `optipng` and `advpng`

This reverts commit d8f82e67.

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