Merge pull request #20 from kaeza/master

Various Fixes
Ran all textures through pngcrush.
Ran all textures through pngquant.
Lower resolution of roof slopes/corners from 256 to 16.
forgot to check for proper tiling between segments.  fixed.
Made all gates open/close any gates above and/or below if same type.
Reduced hear distance for doors and gates
Only remove fences and signs from inventory if expected
Merge pull request #21 from Zeg9/signs

In creative mode, don't remove fences and signs from inventory when you place them
fix duplication bug in lighting (forgot to return itemstack)
fixed missing itemstack fields in on_rightclick calls in lights/doors
Fixed missing check for ownership/node protection in lights
made lights check for buildable_to instead of just air
corrected the syntax of the sound play commands for gates/doors
add colon to sign, minor tweak to semicolon texture
Fix inverted conditional that prevents microwaves from working
Tweak infotext of microwave to say "Microwave is ..." instead of "Furnace is..."
More infortext tweaks
Test
Add decorative window-unit air conditioner
also, renamed nodes.lua -> misc_nodes.lua
Phased out all deprecated minetest.env:* uses in favor of minetest.*
minor tweak to slab and quarter-slab glowlights - better top/bottom textures