Add on_ignite functions to tnt, gunpowder, coalblock.

A deeper, darker level of leaves is created by tiling the texture
2 by 2, reducing brightness and offsetting this.
For a denser leaf appearence with the 'simple leaves' setting.
Also used for acacia bush leaves.

Selection box width is limited to 14 / 16 node to visually
distinguish box from any neighbouring cubic nodes.

Edited fuels: fences, wooden ladder.
New fuels:
boat, paper, book, dry shrub, stick, vessels shelf, wooden tools,
wooden door, trapdoor, fence gates, farming crops, stairs, slabs, beds.

Some code simplifications.

The purpose of this is to allow mods to be able to interact (e.g. fill up)
an empty bucket when it is used to punch a node that's not a liquid source
or when punching a custom entity (e.g. milking a cow).

- Use opaque texture for top+bottom of iron bar
- Add color variation for iron bar top/bottom
- Add paramat's texture to credits
- Update license info for paramat's textures

This plays when damage is disabled, an engine bug.
We can remove it because both sounds are identical, now it is removed
the 'player damage' sound still plays when falling damage is taken.

To allow mapgen bushes in green-grass and savanna grasslands.
Nodes for a generic bush and an acacia bush.
Stem nodes are craftable to a single wood node to provide a small
amount of wood resource in grasslands.
Fuel times are that of corresponding 'wood' nodes, 1/4 that of
corresponding tree nodes.
No leafdecay to enable use as hedges or without a nearby tree trunk.
Uses 'default leaves simple' texture for extra visual thickness.

Use 'player damage' sound for both damage and falling damage.
Gains for damage sounds are set in the engine, however we cannot change
those gains as other subgames already use damage sounds based on those
gains.
Sound has been re-edited from source and normalised to 0 dB for
maximum volume, which is only just enough because gain is fixed at 0.5
in the engine.

The check for igniters (fire/lava) will be performed every 10 secs
if the item is flammable.

if the item is found to be in lava it will then burn up and
disappear in a smoke puff.

If a non-lava igniter node is found, a combination of `flammable`
value of the item and `igniter` group value of the node will be used
to determine the chance for the item to be removed.

'jungleleaves simple' had completely different leaf colours to
'jungleleaves', now matched.
'leaves simple' had dark green instead of black colour for transparent
pixels (the 'leaves' texture uses black), normally these pixels would
not be rendered as opaque colours but bush nodes now use this texture
and will be rendering it as opaque. The dark green pixels resulted in
a texture lacking in contrast.

Original code by Sofar.
Textures by Pithydon.
Exposure to air converts live coral to coral skeleton.
Live corals drop coral skeleton.

River water needs to be 'liquid_renewable = false' to avoid a mess caused by
spreading of sources, however picking it up with a bucket then creates
a hole in the river. Allow a 'force-renew' of the source node if it has a
source neighbour.

Handy for when modders want to use these definitions to extend or add to the mod

Pass nodename to tnt.burn function where possible to reduce
use of 'get_node'.
Change 'ipairs' to 'pairs'.
Use 'nodeupdate_single(pos)' instead of 'nodeupdate(pos)' to
avoid every node triggering recursion, the loop itself takes
the place of recursion and works upwards through horizontal
planes as required.

Through testing the chance is changed to 50 such that grass spread
speed matches that of the previous (0.4.13) ABM version.

Credit to tenplus1 for the suggestion to generalise for mod use.
Mods can add mod nodes to 'group:spreading_dirt_type' enabling the
function to work with mod nodes.

Add some nodes to this group.

Removing 'dirt_with_grass' etc. from 'neighbors' stops the ABM action
running everywhere and constantly, on the dirt nodes immediately below
the surface nodes. Now the action only runs in the rare case of a dirt
node with neighbouring air, grass decorations or snow.

Remove check for air above to allow grass to spread under light-
transmitting nodes such as fences, walls, plants. This causes spread
under slabs, stairs and glass, when near air, but seems worth it.

Remove unnecessary check for nil node.

Rotating doors with screwdrivers causes too many issues to be worth it.

This removes the group overrides for dirt, dirt_with_grass and dirt_with_dry_grass which aren't needed and interfere with new grass spreading changes: https://github.com/minetest/minetest_game/pull/1286

Commit originally by PilzAdam.
Settings appear in advanced settings menu.

The collision box still extended into a neighbouring empty node, causing
falling node objects to collide but not transform back into normal nodes.
Completes the fix started in a previous similar commit.

From PixelBOX2 texture pack.
Brightness increased for 'snow' and 'snow side'.