This was done to clean up the license and to ensure that any commercial fork of the engine has to obey the far stricter requirements concerning source distribution. The old license was compatible with GPLv2 whereas combining GPLv2 and LGPLv3 force a license upgrade to GPLv3. The license of code that originates from ZDoomGL has not been changed.
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.
