Looking at the backup dates for files in <mdl.int>, mdl106.exe is from
20th January 1981, whereas some of the source files are from a couple of
years later. Revert to the last version prior to 20th January 1981 -- in
every case, this was the earliest revision that was kept in <mdl.int>.
This undoes the changes that we'd previously made to these files, many
of which are no longer necessary now that we're using MIDAS 73.
