Run sage-upgrade *outside* of the Sage shell

[jdemeyer]

Running make inside a Sage shell doesn't really work well, because sage-env isn't resourced during the build. This breaks upgrading if new packages are installed in the upgrade which require environment variable changes. Most of the old work-arounds in spkg/install removed in #14715 existed precisely for this reason.

Now that nothing can upgrade to Sage 6.0, we should make sure that upgrading from Sage 6.0 doesn't suffer this problem.

Depends on #14715

CC: @vbraun @ohanar

Component: build

Author: Jeroen Demeyer

Branch/Commit: u/vbraun/ticket/15517 @ 1f27435

Reviewer: Volker Braun, R. Andrew Ohana

Issue created by migration from https://trac.sagemath.org/ticket/15517

[jdemeyer]

Dependencies: #14715

[jdemeyer]

Description changed:

--- 
+++ 
@@ -1,3 +1,3 @@
-Running `make` inside a Sage shell doesn't really work well, because `sage-env` isn't resourced during the build. This breaks upgrading if new packages are installed in the upgrade which require environment variable changes.
+Running `make` inside a Sage shell doesn't really work well, because `sage-env` isn't resourced during the build. This breaks upgrading if new packages are installed in the upgrade which require environment variable changes. Most of the old work-arounds in `spkg/install` removed in #14715 existed precisely for this reason.
 
 Now that nothing can upgrade **to** Sage 6.0, we should make sure that upgrading **from** Sage 6.0 doesn't suffer this problem.

[jdemeyer]

Branch: u/jdemeyer/ticket/15517

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

[bcd9b51](https://github.com/sagemath/sagetrac-mirror/commit/bcd9b51)

Create sage-update script, split off from sage-upgrade

[sagetrac-git]

Commit: bcd9b51

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

[6298111](https://github.com/sagemath/sagetrac-mirror/commit/6298111)

Source sage-env before "set -e"

[sagetrac-git]

Changed commit from bcd9b51 to 6298111

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

[3709390](https://github.com/sagemath/sagetrac-mirror/commit/3709390)

Pass arguments to sage-update

[sagetrac-git]

Changed commit from 6298111 to 3709390

[jdemeyer]

comment:7

In theory, this needs_review, but I don't manage to test upgrading because I don't know what command line to give to sage -upgrade.

[vbraun]

comment:8

There is no need to name a temporary branch, you can just work with commits:

git fetch trac master
git merge --ff-only FETCH_HEAD