Make research got_tech_multi mandatory in new savegames
savegame3.c currently considers research got_tech_multi an optional field, because it was not saved by older S3_0 versions.
Add compatibility conversions (3.1 -> 3.2, older dev version -> current dev version) to add the field, and make savegame3.c to consider it mandatory.
As part of #43200, this has also been posted to http://forum.freeciv.org/f/viewtopic.php?f=14&t=92107
savegame3.c currently considers research got_tech_multi an optional field, because it was not saved by older S3_0 versions.
Add compatibility conversions (3.1 -> 3.2, older dev version -> current dev version) to add the field, and make savegame3.c to consider it mandatory.
As part of #43200, this has also been posted to http://forum.freeciv.org/f/viewtopic.php?f=14&t=92107