cherry-pick of several intermediate commits.
  00685293 from Thu Jul 4 11:00:48 2019 +0200.
  9386c13a from Thu May 16 08:09:25 2019 +0200
  3813e316 from Fri May 10 16:56:23 2019 +0200
  50ee0275 from Sun May 5 10:19:47 2019 +0200
  0b54af76 from Sat May 4 20:04:48 2019 +0200
  d07f97d1 from Sat May 4 15:30:37 2019 +0200
  e924c740 from Sat May 4 15:21:27 2019 +0200
  e3138dad from Sat May 4 14:00:44 2019 +0200
  a58a53c1 from Fri May 3 16:42:26 2019 +0200

ILP model: save latest version.

Many a long night was spent hacking on this.
Deadlines where tight.
Midnight oil was burnt.
So I didn't commit intermediate stages.