Fix Doom 3 BFG's broken Doom 2 MAP33 Betray.

Doom 3 BFG Edition includes an extra secret Doom 2 level called "MAP33: Betray", originally from the Xbox Doom 3 Collector's Edition. It is supposed to be accessed from a secret exit in MAP02. But due to a bug in Doom 3 BFG Edition, that secret exit just takes you to the next level like the normal exit.

Note, Doom 3 BFG Edition does not include the Doom 1 equivalent, E1M10: Sewers.

This patch by Carl Kenner fixes the source code so that:
The secret exit in MAP02 takes you to MAP33 like it's supposed to.
The console command "idclev 33" will also take you there.
The exit in MAP33 takes you back to MAP03.
MAP33 won't crash the game.
MAP33 has the right name when you save the game.
MAP33's bug of the missing teleporter tag near the yellow door is fixed.
The Wolfenstein SS in MAP33 are replaced with Former Humans.

No changes to the WAD files are needed.
Merge pull request #1 from CarlKenner/fix-map33-betray

Fix Doom 3 BFG's broken Doom 2 MAP33 Betray.