buildbot/buildbot — pull request #503 by yetanotherion (2012-08-23 16:07:08+00:00)
Title: interrupt seems not to release step locks

the interrupt method in the buildsteps does not release
locks related to the buildsteps.

this commit aims at correcting the bug and at adding the
unit tests that validate the fix.

Signed-off-by: Ion, Alberdi