celeron55/minetest — pull request #289 by Uberi (2012-11-18 22:59:59+00:00)
Title: Fix trees growing into any type of node

0gb.us had [discovered a while ago](http://minetest.net/forum/viewtopic.php?pid=48897#p48897) that tree trunks can grow into any type of node.

This has recently become an issue when it started being [used to grief servers](http://webcache.googleusercontent.com/search?q=cache:9LPjJU_6JmcJ:minetest.net/forum/viewtopic.php%3Fid%3D3693+&cd=1&hl=en&ct=clnk). As it circumvents the rollback mechanism, it's pretty obvious how this is a serious problem.

I made a quick fix for the issue that allows the tree to grow only in air. The patch was originally posted in #280, but I thought it would be better to submit it separately.