E.g.,

[environment]
PATH.append.literal = "bad/\path\/idea"

"Enable shared dependencies by default" was in there twice.

* Set shared dependencies as the default

* user-changes.md: Explain shared builds

We were attempting to enter a folder that not always will exist.

* Auto-refresh indexes after some time (default 24h)

* ask user on first autoupdate

* User changes

* Test behavior on network failure

* New `alr printenv --last-build`

This may be useful when no direct editing of manifests is convenient, as
otherwise `printenv` will always use the manifest's configuration.

* make new behavior the default with fallback

* CI fixes

* Added `shared-build` driver

* Added `build_mode` key to the Python driver

* Fix config generation in `alr update` in shared mode

* Remove need for compiler in absence of dependencies

* Fixed monorepo tests and base dir

* Delay config generation in sandboxed mode too

* Include explicit switches in build hash inputs

This is necessary because for shared builds we're never regenerating the
configuration, so changes in switches went undetected

* Require complete config for sandboxed build

* Self-review

* Update new tests

* Remove ".git" after cloning, with option to disable

Also make clones shallow (they already were for pins)

* Fix test

* Omit global switches in subcmd-specific help

* Update clic dependency

* Remove ".git" after cloning, with option to disable

Also make clones shallow (they already were for pins)

* Fix test

* Omit global switches in subcmd-specific help

* Update clic dependency

user-changes.md: Explain shared builds

Added `shared-build` driver

Added `build_mode` key to the Python driver

Fix config generation in `alr update` in shared mode

Remove need for compiler in absence of dependencies

Fixed monorepo tests and base dir

Delay config generation in sandboxed mode too

Include explicit switches in build hash inputs

This is necessary because for shared builds we're never regenerating the
configuration, so changes in switches went undetected

Require complete config for sandboxed build

Self-review

Supersedes #1457

Fixes #1456

* Fix a couple of bugs related to new build system

* Test for the fixed bug

* Self-review

* Omit default mention in shared deps help

* Remove Export_Env arguments all-around

Now that we delay all actions to build time, we can set environment just at
that time and avoid complications.

* Debug workflow and dependency hashes

* Self-review

* Fix bug in solution traversal related to linked releases

* New test

* CI fixes

This fixes #1402.

* Add traceback enabling env var

* Test for new config var

* Refactored flags into new crate

* Delay post-fetch to first build (ensures complete env)

* Folderize flags

* Self-review

* Simpler flag use, better encapsulation

* Fix Windows-only test

Since a dependency may use different specs based on config values, environment
variables, GPR externals... we include the hash of dependencies in dependents'
hash inputs.

* Regenerate configs on demand (sandboxed deps)

Leverage the new build hashing to make sure when a configuration needs
regenerating. This is pessimistic but safer than what we had, and more
future-proof.

* fix wrong switches generation

* test fixes

* New test, checking no unneeded rebuilds happen

* Fixes for CI-detected issues