Check Engine

Crash Doctor understands three more kinds of crashes:
- "Registered twice" crashes (like "Duplicate client extensions registration for Block{create:belt}"): it says which thing was added twice and why: the mod is installed twice, something made its setup run twice, or an addon made for a different version adds the same thing. With the fix.
- Mixin clashes: when two mods patch the same game code, it now names both of them instead of just one, and tells you to update both or remove one.
- Random timing crashes: big packs set mods up in parallel, and sometimes two mods break a shared list at the same moment (like ChillOut with Player Animator). Crash Doctor now says it's random and to just launch again, and the pre-launch window no longer warns "will probably fail again" for it.