Linux build jobs on Travis CI skip the P4 and Git LFS tests since
commit 657343a60 (travis-ci: move Travis CI code into dedicated
scripts, 2017-09-10), claiming there are no P4 or Git LFS installed.

The reason is that P4 and Git LFS binaries are not installed to a
directory in the default $PATH, but their directories are prepended to
$PATH.  This worked just fine before said commit, because $PATH was
set in a scriptlet embedded in our '.travis.yml', thus its new value
was visible during the rest of the build job.  However, after these
embedded scriptlets were moved into dedicated scripts executed in
separate shell processes, any variable set in one of those scripts is
only visible in that single script but not in any of the others.  In
this case, 'ci/install-dependencies.sh' downloads P4 and Git LFS and
modifies $PATH, but to no effect, because 'ci/run-tests.sh' only sees
Travis CI's default $PATH.

Move adjusting $PATH to 'ci/lib-travisci.sh', which is sourced in all
other 'ci/' scripts, so all those scripts will see the updated $PATH
value.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

09f5e97 ("travis-ci: skip a branch build if equal tag is present",
2017-09-17) introduced the "skip_branch_tip_with_tag" function with
a broken string comparison. Fix it!

Reported-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

If we push a branch and a tag pointing to the HEAD of this branch,
then Travis CI would run the build twice. This wastes resources and
slows the testing.

Add a function to detect this situation and skip the build the branch
if appropriate. Invoke this function on every build.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Most of the Travis CI commands are in the '.travis.yml'. The yml format
does not support functions and therefore code duplication is necessary
to run commands across all builds.

To fix this, add a library for common CI functions. Move all Travis CI
code into dedicated scripts and make them call the library first.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* ls/travis-relays-for-windows-ci:
  travis-ci: retry if Git for Windows CI returns HTTP error 502 or 503
  travis-ci: handle Git for Windows CI status "failed" explicitly

Travis CI gained a task to format the documentation with both
AsciiDoc and AsciiDoctor.

* ls/travis-doc-asciidoctor:
  travis-ci: check AsciiDoc/AsciiDoctor stderr output
  travis-ci: unset compiler for jobs that do not need one
  travis-ci: parallelize documentation build
  travis-ci: build documentation with AsciiDoc and Asciidoctor

Typofix.

* rg/a-the-typo:
  fix minor typos

The Git for Windows CI web app sometimes returns HTTP errors of
"502 bad gateway" or "503 service unavailable" [1]. We also need to
check the HTTP content because the GfW web app seems to pass through
(error) results from other Azure calls with HTTP code 200.
Wait a little and retry the request if this happens.

[1] https://docs.microsoft.com/en-in/azure/app-service-web/app-service-web-troubleshoot-http-502-http-503

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Git for Windows CI returns "completed: failed" if a build or test
failure happened. This case was processed as "Unhandled status".
Handle the case explicitly.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>