See: https://github.com/minetest/minetest/issues/1525

Background
Wuzzy2: If you attempt to spawn a L-system tree with minetest.spawn_tree, you can make Minetest crash if it is attempted to pop an empty stack.

ShadowNinja: This shouldn't cause a segmentation fault, but it should throw a Lua error

Commit Description
This commit throws a Lua error instead of causing a segmentation fault. The server will still "crash" but will include a Lua backtrace.

L-Systems fix randomness
Unless a random seed is provided (via Lua treedef) seed the PRNG with a different seed for each tree
Resolves: https://github.com/minetest/minetest/issues/1469

Fix l-system crash when treedef random_level not set by Lua

Config settings:
profiling = true/false (gather statistics)
detailed_profiling = true/false (break mod times to callbacks)

Chat commands:
save_mod_profile saves current statistics in debug.txt and shows on console (on default loglevel)

There have been plenty of ppl involved in creating this version.
I don't wanna mention names as I'm sure I'd forget someone so I
just tell where help has been done:
- The partial android versions done by various ppl
- Testing on different android devices
- reviewing code (especially the in core changes)
- testing controls
- reviewing texts

A big thank you to everyone helping this to be completed!

Separate element for tooltips. Delayed showing,
use global color or given ones.

Fix crash on using cursor keys in client menu without selected server
Add support for non fixed size tabviews

Add DPI support for statbar
Move heart+bubble bar to Lua HUD
Add statbar size (based upon an idea by blue42u)
Add support for customizing breath and statbar

Add support for (configurable) multiline hotbar
Improved screensize handling
Add userdefined gui scale by BlockMen

Don't use TOSERVER_RECEIVED_MEDIA but TOSERVER_CLIENT_READY as indicatio for client ready
Handle clients with protocol version < 23 (almost) same way as before
Make client tell server about it's version
Add client state to not send bogus player position updates prior init complete
Add access to statistics information (peer connction time,rtt,version)
Fix clients standing stalled in world while preloading item visuals (new clients only)
Add get_player_information to read client specific information from lua

Remove flagmask field from set_mapgen_params table
Add small bits of needed documentation