Merge branch 'ls/travis-scriptify'

The scripts to drive TravisCI has been reorganized and then an
optimization to avoid spending cycles on a branch whose tip is
tagged has been implemented.

* ls/travis-scriptify:
  travis-ci: fix "skip_branch_tip_with_tag()" string comparison
  travis: dedent a few scripts that are indented overly deeply
  travis-ci: skip a branch build if equal tag is present
  travis-ci: move Travis CI code into dedicated scripts