Only Award Bonuses / Record Attack Emblems from Physically Beating a Level

This merge request fixes the non-cheat half of #1104 (closed) by only awarding score bonuses and record attack emblems to those who physically beat a level proper. If in multiplayer, you exit the level without having beaten it, such as from exitlevel or playersforexit, you will not be rewarded them. The PF_FINISHED flag has been used to determine this, and will now get set in all instances of proper level finishing. P_DoPlayerExit now has a second parameter to determine whether this flag is applied or not, which is true by default in Lua.

Test exe: finishfix.exe