#247 sector friction not preserved between save/reload

[rbk]

Hi there!

I noticed a (possibly really old, possibly intentional?) quirk that prb+ doesn't retain friction properties of sectors in between game save/reloads.

The short version: Toggling "force_prboom_friction" in e6y.c seems to revert back to the original thinker-based method, and works as expected between save/loads. The modified sector property method isn't preserved, but perhaps this information could be appended to the savegame archive in a similar fashion as other sector attributes?

The long version (with some demonstration videos, and more of my rambling):
https://www.doomworld.com/vb/post/1707117
https://www.doomworld.com/vb/post/1707258

Cheers!
-R