Root safety-checking

Fixes #9117.  Thanks to Rivet and  Kyriolexical Dino for reporting.
Express safety-lock

As requested.
Saprophage fixes

Because you're gonna be a while waiting for your clean water to rot.  XD
Refactor game::throw_item
Fixes some stupidity I made
Comments
Nitpicking on math
Merge pull request #9118 from KA101/soilfocus

Root safety-checking
Merge pull request #9131 from EpicOrange/upgrade-code

Moved around code in game::throw_item
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.
Make sure pointers are initialized.
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.