[META issue] Backport release: 2.1.3

[kit-ty-kate]

Fix PRs

• Optimisation for partial installability queries #4882
• Improve performance of some opam list combination #4999
• Actually permit multiple state caches to co-exist #4934
• Improve performance of opam show by 300% when the package to show is given explicitly or unique #4998
• Depexts: Stop zypper from upgrading packages on updates on OpenSUSE #4978
• Print user-friendly error messages when a command is not found, before calling the sandbox #4971
• Move cold compiler on master to 4.13.1 #5017
• Fix empty conflict explanations #4982
• Fix make doc #5030
• Fix 'opam init' and 'opam init --reinit' when the jobs variable has been set in the opamrc or the current config #5056
• Github deprecation of git:// protocol updates #5097
• Fix make doc #5030
• opam var and opam option fixes when no switch is installed #5027
• Bump opam-file-format to 2.1.4 #5117
• _Correct_ trying to be too clever when upgrading switches from opam 2.0 #5176
• Fix auto pinning and depext handling #5047
• Fix working dir checkout #4879
• shell/bootstrap-ocaml.sh: do not fail if curl/wget is missing #5223
• Improve warning wording if curl/wget is not present #5233

Reftests updates

• Fix admin repo upgrade internal error #4965
• updates on reftests #4913
• Reftests: some updates #4966
• Reftests: port opam-rt tests #4979
• Irons out a few kinks left by latest reftest improvements #4974
• reftest: Escape regexps characters in string replacements primitives #5009
• Some new tests, and auto-update after package def #5004
• Add pre-processing to coinstallability checks #5024 (very partial)
• Add lock test #4963
• Make OpamConfigCommand.global_allowed_fields fully lazy #5162
• reftests: update for cmdliner.1.1.1 #5131

TODO

[AltGr]

woohoo issue #5000 ! 🎉

[rjbou]

released! 🎉