This, from the CVS log, from June 19, 2008:

--------------------------------------------------------------------------------

version 1.0 and demo wad files support:

the demo wad file support doesn't need a special configuration anymore.
besides, the --enable-demowad configuration option isn't an end-user
switch anymore:  it makes the compiled binary to work only with demo
(PC or Mac) version wad files and error-out otherwise.

The striking difference between versions 1.0 and 1.1 is the MAXPLAYER
change: 1.0 supports 4 and 1.1 supports 8 players, and this results in
subtle problems.

added new configuration option, --enable-oldwad :  compiles the exe to
specifically use the 1.0 (shareware or retail) wad files, 1.1 wads are
rejected and errors out.  it configures the engine to MAXPLAYERS == 4
instead of the normal 8 value.

Saves across different versions are not compatible. We are now signing
saves made with binaries configured with the oldwad option with 2.36
instead of 2.37: 2.36 is the signature which the 1.0 version used, but
remember, this doesn't mean the saves from those old dos versions are
supported, they are NOT.  The normal 8-player binary will sign the saves
with 2.37 as usual, and it will not care about with which wad it is
running with.

The worst thing is the recorded demos:  since there are no versioning
mechanisms, the demos saved with 4-player and 8-player versions are
incompatible.  I hacked a few things here:  basically, if a version-1.0
wad is detected, demo playback and recording is done according to 4
players.  but this isn't accurate, either (see procedures G_RecordDemo
and G_DoPlayDemo.)

in short, it seems like there are no problems with the binaries configured
with the oldwad option (the 4-player binaries).  but if one is running
the normal 8-player binary with a 1.0 wad file, there may still be problems,
especially in the multiplayer code which we can't test at the moment.

another option would be to make the 8-player binary to error out with
version 1.0 (demo or full) wad files.  I'm open to ideas.

