Rogue fixed DOOM bug regarding switch sound origins

Re-examination of assembly reveals use of &line->frontsector->soundorg
instead of buttonlist->soundorg.
Another teleport beacon correction

Flag to be cleared is MF_SPECIAL, not MF_SOLID (verified against
disassembly). Otherwise you get to spawn an infinite number of rebels
from one beacon. Not to mention, it isn't SOLID to start with.