MacOS X doesn't have '/bin/true'
Revert "Travis config trial: git config --global"

Avoids messing with global config when running the script
manually on a developer machine.

This reverts commit 6225092355e3087c3e73928f54cc1073c55067d6.
travis-doxygen.sh: allow overriding GitHub repo from environment
Merge branch 'travis-ci' into github
explicitly configure credential helper
.travis.yml: use personal Travis CI instance