This solves the most severe occurences of sprites being drawn in front of a portal's contents. It is not a full fix, though, there's still some extreme cases where portals may glitch if some stuff gets between the camera and the actual portal area.
Normally this has to perform a full check of the subsector against the portal's camera-facing linedefs but that's too costly for those rare cases where it may be an issue.
The software renderer float conversion removed viewx and viewy which are still needed for efficient position checks against nodes without constant float->fixed conversions.
