Merge branch 'sg/travis-build-during-script-phase' into maint

Build the executable in 'script' phase in Travis CI integration, to
follow the established practice, rather than during 'before_script'
phase.  This allows the CI categorize the failures better ('failed'
is project's fault, 'errored' is build environment's).

* sg/travis-build-during-script-phase:
  travis-ci: build Git during the 'script' phase