The reason for defining them is to be able to fill out the Eternity translation table for GZDoom's Extradata parser.
Most of the new specials are mere specializations of ZDoom's Generic_* functions and occupy positions above 255 to avoid filling up the last remaining free slots available for Hexen format maps.
Allowing action specials greater than 255 required a few changes:
* all access to action specials is now through a small set of access functions.
* Two new PCodes were added to ACC to handle these new specials from scripts.
* a minor change to the network protocol, so netgame and demo version numbers were bumped.
* FS_Execute is now properly defined in p_lnspec.cpp.
Two of the newly added specials - generalizations of the special 'close Door in 30 seconds' and 'raise door in 5 minutes' sector types, will also be available to Hexen format maps. The rest are limited to use in ACS, UDMF and DECORATE.
This also adds 'change' and 'crush' parameters to most Floor_* and Ceiling_* specials, again to match Eternity's feature set.
