Some slope improvements/fixes
Dear Red, I did some things.
- Made the slope flag SL_NOPHYSICS actually have an effect like we wanted to, but didn't get around to implementing yet - activated by setting the slope's linedef flags to have ML_NOSONIC.
- Made downhill slope thrusts proportional to an object's gravity.
- To make the above happen - seperated out the gravity value finding code in P_CheckGravity into a seperate function, P_GetMobjGravity. (p_mobj.c, .h)
- Turned those PANIC n console messages (which would inevitably be followed up with a crash, since we're accessing invalid memory immediately after) into a descriptive I_Error.
- Put the SRB2CB type-shimming behind an ESLOPE_TYPESHIM ifdef.
- Removed SPRINGCLEAN-ifdef'd code.
- Cleaned up some eosteric comments.
Current testing file available at /toaster/slptst3.wad on the ftp.
I want to do more to the branch like implement SL_ANCHORVERTEX in the near future, but I need to go for the night and this is probably safe to merge in its current state.