100% server cpu 100ms frametimes with stuck entities

This happens when sv_gameplayfix_slidemoveprojectiles 1 and the stuck entity uses a TOSS-based movetype and the first plane it's in collision with isn't walkable. It was worked around for badly placed pickup items with 31f72590 but can still occur, eg with flags and dead vehicles.

A fairly easy way to reproduce in 0.8.6 is

1. Load catharsis and get a flag
2. Latch crouch, eg by getting in a place under the stairs where you can only fit by crouching
3. prvm_edictset server 1 origin "-1116.78589 267.681061 106.271767"
4. Look straight down, drop flag, try to move away so as not to pick it up again
5. ????
6. big lag

!1234 (merged) will prevent that particular method by making it impossible for flags to be stuck when dropped.

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This doesn't seem to need any special steps to reproduce apart from loading the map, I used a dedicated server. Xonotic 0.8.5 doesn't have this issue.

Git bisect says it was introduced by dc43859d