Update on Geant4

[Stephan Lachnit <stephanlachnit@protonmail.com>]

Small update regarding Geant4:

Geant4 10.7.0 got released in December, which is basically lintian clean so far (thanks to upstream for fixing all that).
However, Geant4 10.7.0 won't make it into Bullseye (or even Sid for that matter), because there is a major problem: it segfaults.

I tried it on 3 different setups, one running Ubuntu 20.10, and it justs segfaults every time one starts a run.
I don't know why (yet), I *think* it might be due to the introduction of PTL & TBB, but I haven't debugged it yet.

PTL is a library which should heavily increase performance, but it is really new and upstream has stabilized just yet.
I hope the next major Geant4 release (i. e. 10.8.0) uses the just released upstream PTL 1.0.0, so we can use that.

For anyone interested, my current plan is to package PTL and wait for the next minor Geant4 version (10.7.1) before trying to debugging it.
If you want to help, you can try to find out why it segfaults (requires to start a run, you can take any included example).

Regards,
Stephan