This fixes a long standing and until now unnoticed bug with negative
colored dynamic lights. Since we never set the OpenGL renderer as out
renderer, remaining softrenderer code was executed and the corresponding
effects never rendered. This manifested itself in missing darkness
around the "gravity well" in rogue.
If "horplus" is set, the "fov" cvar is interpreted as the horizontal FOV
in a 4:3 screen, and is adapted automatically to the current screen
aspect ratio accordingly. If not set, use the old Vert- approach.
In addition, "horplus" can also be set from the video menu by selecting
the "Auto" option for aspect ratio, which also resets the FOV value to the
standard 90 degrees.
Finally, add a 5:4 aspect ratio (1280x1024) and correct the 16:9 angle
slightly.
