doom: Add -noiwaddeh command line parameter.

Both the Freedoom IWADs and the rereleased HACX IWAD contain embedded
DEHACKED lumps that are automatically loaded on startup. However,
there may be some situations where it is undesirable to load these
patches - when loading certain mods such as BTSX, for example. For
these cases, allow the user to override the default behavior with a
command line parameter.