Make targets in the Makefile part of PHONY.
Don't overwrite $DOKKU_ROOT/{HOSTNAME,VHOST}
Enable tracing in hooks when DOKKU_TRACE is set.

This makes it much easier to debug plugins.
Also source the 'dokkurc' file when starting dokku. This makes it easy
to define DOKKU_TRACE over ssh.
Enable DOKKU_TRACE when running travis tests.
Merge pull request #317 from plietar/master

Enable tracing in hooks when DOKKU_TRACE is set.
Merge pull request #309 from plietar/make-phony

Make targets in the Makefile part of PHONY.
Reenable PHP test
Merge pull request #318 from rhy-jot/2013-11-18/reenable-php

Reenable PHP test
Revert "Reenable PHP test"

This reverts commit 7ecacd5d98295bef0ec63866a9b1a083655536a9.