Changes skill in weldrig recipe to use mechanics.

Most of the books that contain it are mechanics or electronics books,
and the skill it uses is mechanics, not fabrication.
Made pillows require both components.
tabkiller 4: mall
Also fixed down blanket.
Stupid keys being nearby. Fixed typo.
More helpful debug/too-much-ammo-spawned message.

I've not actually seen this debug message happen, but assuming it ever
does, it'd be nice if it told you how much ammo was too much, instead of
giving you the count after clamping.
Add some flags modifying collisions to various furniture.
Misc whitespace and include tweaks.
Smash items when a vehicle wheel runs over them.
Use a bitmask instead of string flag for a wheel check.
Avoid smashing furniture if it has nocollide flag, and avoid smashing tiny furniture unless it's hit by a wheel.
Made forge transparent
Alters zombified dogs' speed ratings.

After hearing a lot of complaints about the various zombie dogs I
decided to look into their numbers. Everything looked fine except for
their
speeds, which were pretty crazy values.

Keep in mind that a normal, living dog has a speed of 150 and a normal
zombie dog has a speed of 105.

Stuff I changed:

skeleton dog had speed 160 which I reduced to 125
Z-9 and rot-weiler had speed 150 which I reduced to 105
Add short flag to some more terrain and furniture.
Document the new terrain/furniture flags.
Make vehicle protrusions not interact with short terrain.
Merge branch 'bonedog-speednerf' of https://github.com/Rivet-the-Zombie/Cataclysm-DDA into merge2
Merge branch 'vehicle-collision-tweaks' of https://github.com/kevingranade/Cataclysm-DDA into merge2
Merge branch 'forge' of https://github.com/Mshock777/Cataclysm-DDA into merge2

Conflicts:
	data/json/furniture.json

Fixed again.
Merge branch 'how-much-did-you-say' of https://github.com/narc0tiq/Cataclysm-DDA into merge2