templater: add wrapper for a single template mapping This can be used to nest template mappings without inserting a sequence-like layer. See the next patch for example.

templatekw: extract internal "{rev}:{node|formatnode}" template to constant This will be used later.

tweakdefaults: remove commands.resolve.mark-check=abort, it is too broken See issue6020 for the current case. I don't want to continue attempting to fix this on the stable branch, so I'm removing from tweakdefaults and will send fixes meant for the default branch and 4.9. Differential Revision: https://phab.mercurial-scm.org/D5225

resolve: when resolve.mark-check=abort, downgrade to warning if pats specified Previously, with --config resolve.mark-check=abort, running `hg resolve -m foo` would abort and emit a message saying to use --all. This command does not work, though: `hg resolve -m foo --all`, and it's really weird for --all to be the "--force" flag. My original goal with the option was to make it so that `hg resolve -m` (no filename arguments) was safer, which is why --all is used; in my mind, `hg resolve -m foo` should always mark it as resolved, and `--all` is how you specify "all the files", so that's why I chose `hg resolve -m --all` as the way out of `hg resolve -m` aborting. This commit makes all of this work the way it was meant to in my head :) Differential Revision: https://phab.mercurial-scm.org/D5218

test: remove changes preparing the drop of `HGMERGE` These changes are no longer necessary so we better drop them.

run-tests: define the default merge tool through configuration Using the `HGMERGE` environment variable generates confusion as it overrides any value set through configuration. By setting the default value through the default HGRC, the usual overriding rules apply and it should reduce confusion.

run-tests: explicitly declare the list of dropped environment variable It will make the list clearer and more maintainable.

test: drop usage of `HGMERGE` in `test-lfconvert.t` Using configuration instead of environment variable has a strange effect on the output, but no impact on the end result.

test: drop usage of `HGMERGE` in `test-merge-types.t` Using configuration instead of environment variable has a strange effect on the output, but no impact on the end result.

test: use the "correct" merge tool in `test-rebase-detach.t` The value of `HGMERGE` overrides the value passed through --config. We are about to drop this `HGMERGE` environment variable so we update the value used in config to match what is currently in use. This is another example of confusion introduced by the `HGMERGE` environment variable.