Gracefully break upgrading from earlier versions

[jdemeyer]

If older versions of Sage try to upgrade to Sage 6.0, this should break gracefully. There should be a nice message explaining that it cannot be done, perhaps pointing to http://boxen.math.washington.edu/home/release/sage-5.13/ where the upgrade to Sage 5.13 can be done.

Depends on #14232
Depends on #14754
Depends on #14417

Component: build

Author: Jeroen Demeyer

Branch/Commit: u/jdemeyer/ticket/14715 @ cd83bc9

Reviewer: Volker Braun

Issue created by migration from https://trac.sagemath.org/ticket/14715

[jdemeyer]

Dependencies: #14232

[jdemeyer]

Changed dependencies from #14232 to #14232, #10508

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1 +1,3 @@
 Sage 5.0 was released on 14 May 2012, over a year ago. Dropping support for upgrades from earlier versions can simplify the build system.
+
+**Apply** [attachment: 14715_no_sage_4x_upgrade.patch](https://github.com/sagemath/sage-prod/files/10657918/14715_no_sage_4x_upgrade.patch.gz) to `SAGE_ROOT`.

[jdemeyer]

Changed dependencies from #14232, #10508 to #14232, #10508, #14417

[jdemeyer]

Author: Jeroen Demeyer

[jdemeyer]

comment:6

Attachment: 14715_no_sage_4x_upgrade.patch.gz

[jdemeyer]

Changed dependencies from #14232, #10508, #14417 to #14232, #14754, #14417

[vbraun]

Reviewer: Volker Braun

[vbraun]

comment:7

Looks good to me