Remove gamemission variables for Heretic and Hexen and hard-code to the
appropriate values.

Subversion-branch: /branches/v2-branch
Subversion-revision: 2708
Remove call to I_SetWindowTitle() that is no longer needed.

Subversion-branch: /branches/v2-branch
Subversion-revision: 2709
Rip out special casing on Windows that defaults to the SDL directx
driver over the Windows GDI one. This causes far too many problems.

Subversion-branch: /branches/v2-branch
Subversion-revision: 2710