Define `__file__`, when interpreting `buildbot.tac`.
Merge branch 'runner-__file__' into buildbot-0.8.8

Conflicts:
	master/buildbot/scripts/base.py
Fix usage of path_module in master-side repo step.
Move some dangling release notes.
Update release notes.
Merge v0.8.8 into master.

Conflicts:
	master/docs/relnotes/index.rst