* src/cuirass/specification.scm (sexp->channel): Ignore channel introduction.

The Guix version of sexp->channel doesn't support the branch field.

* src/cuirass/specification.scm (sexp->channel): New procedure.
* src/cuirass/database.scm (db-get-specifications): Use it.

* bin/evaluate.in: Fix it.

* bin/evaluate.in (checkouts->channel-instances): Remove it.
(instances->cached-profile*): Rename it into ...
(channels->cached-profile): ... this procedure.
(main): Adapt it.

* src/cuirass/specification.scm (channel->sexp): Add channel introduction
support.

* src/cuirass/specification.scm (<build-output>): Set a default path to "".

* src/sql/upgrade-2.sql: Remove it.
* src/sql/upgrade-3.sql: Remove it.
* src/sql/upgrade-4.sql: Remove it.
* src/sql/upgrade-5.sql: Remove it.
* Makefile.am (dist_sql_DATA): Adapt it.

* src/cuirass/logging.scm (log-message): Turn into a procedure.

* README: Update it.

* README: Update dependencies.
* tests/common.scm (pg-tmp): New procedure.
(test-init-db!): Use it.
* tests/database.scm ("db-close"): Do not drop database content.
* tests/http.scm: Ditto.
* tests/metrics.scm: Ditto.

* src/cuirass/http.scm (url-handler): Fix admin specification creation.

* src/schema.sql: Cascade Evaluations, Checkouts and Builds deletion.

* src/cuirass/templates.scm (evaluation-info-table): Improve action button text.

* src/cuirass/templates.scm (evaluation-info-table): Fix action list display.

* src/cuirass/http.scm (url-handler): Add "/admin/evaluation/<id>/cancel" and
"admin/evaluation/<id>/retry" routes.
* src/cuirass/templates.scm (evaluation-info-table): Add "Cancel pending
builds" and "Retry" buttons.

* src/cuirass/database.scm (db-cancel-pending-builds!): New procedure.
* tests/database.scm ("db-cancel-pending-builds!"): New test.

* src/cuirass/database.scm (db-retry-evaluation!): New procedure.
* tests/database.scm ("db-retry-evaluation"): New test.

* README: Explain how to create the test database.

* README: Update it.
* examples/hello.scm: New file.

* tests/common.scm: New file.
* tests/database.scm: Use it.
* tests/http.scm: Ditto.
* tests/metrics.scm: Ditto.

* doc/cuirass.texi (Web API): Update it.
* src/cuirass/http.scm (build->hydra-build): Update it accordingly.

doc/cuirass.texi (Database): Update it.

* src/cuirass/database.scm (db-open): Save the default database in the
%package-database parameter.

* doc/cuirass.texi: Update it.

* src/cuirass/parameters.scm (%cuirass-database, %cuirass-host): New
parameters.
* src/cuirass/database.scm (db-open): Use them.

* src/cuirass/database.scm (db-restart-build!, db-restart-evaluation!): Reset
starttime and stoptime field.

* tests/database.scm ("db-register-builds"): Fix it.

* bin/evaluate.in: Add doc strings.

* bin/evaluate.in (inferior-evaluation): Move profile building to ...
(main): ... here.

* Makefile.am (nobase_dist_pkgdata_DATA): Remove it.
* examples/gnu-system.scm: Remove it.
* examples/guix-jobs.scm: Remove it.
* examples/guix-track-git.scm: Remove it.
* examples/hello-git.scm: Remove it.
* examples/hello-singleton.scm: Remove it.
* examples/hello-subset.scm: Remove it.
* examples/random-jobs.scm: Remove it.
* examples/random.scm: Remove it.

* src/cuirass/database.scm (with-transaction): New macro.

* src/cuirass/remote-server.scm (remote-server): Enable core dump generation.

* src/cuirass/remote-server.scm (zmq-start-proxy): Make sure new messages are
created for each send.

* src/cuirass/remote-server.scm (zmq-start-proxy): Use the message API.

* src/cuirass/remote.scm (zmq-message-receive*): New procedure.
* src/cuirass/remote-server.scm (start-fetch-worker, zmq-start-proxy): Use it.

* src/cuirass/remote-server.scm (zmq-start-proxy): Use copies of message
contents.

* src/cuirass/remote-server.scm (zmq-start-proxy): Print a warning if the poll
loop is blocked for more than 5 seconds.

* src/cuirass/remote-server.scm (start-fetch-worker): Use the message API.

* src/cuirass/database.scm (db-add-build-product): Ignore duplicated
BuildProducts.