This commit introduces the Docker-based local WordPress development environment to the 4.6 branch and converts the Travis test jobs to utilize this environment for easier and more consistent testing.
Until existing blockers with the PHP 5.2 Docker container can be solved, the PHP 5.2 test job will remain using the Travis `precise` image.
Merges [45745,45762,45783-45784,45800,45819,45885,46320,46999,47225,47912,48121,49335,49358,49360,49362] to the 4.6 branch.
See #48301, #47767.
git-svn-id: https://develop.svn.wordpress.org/branches/4.6@49533 602fd350-edb4-49c9-b593-d223f7449a82
