Doc generation is broken due to missing import _

[Steve Baker]

cd doc ; make html # results in the following
Exception occurred:
  File "/home/steveb/dev/localstack/heat/heat/common/exception.py", line 94, in MissingCredentialError
    message = _("Missing required credential: %(required)s")
NameError: name '_' is not defined

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/40768

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/40768
Committed: http://github.com/openstack/heat/commit/0453785f3f7b2a578b433cb0544394aac9bcfb95
Submitter: Jenkins
Branch: master

commit 0453785f3f7b2a578b433cb0544394aac9bcfb95
Author: Steve Baker <email address hidden>
Date: Thu Aug 8 11:20:48 2013 +1200

    Add missing _ imports to allow doc generation

    Fixes bug: 1209413

    Change-Id: I7d405ceb6a500cbb3d0eb19e85cb0540564e0643

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/41554

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/41554
Committed: http://github.com/openstack/heat/commit/3b64fd85190af18d39ca718c9bb11456367e6e80
Submitter: Jenkins
Branch: master

commit 3b64fd85190af18d39ca718c9bb11456367e6e80
Author: Luis A. Garcia <email address hidden>
Date: Mon Aug 12 21:45:46 2013 +0000

    Revert "Add missing _ imports to allow doc generation"

    This change reverts commit 0453785f3f7b2a578b433cb0544394aac9bcfb95 and
    fixes a bug where the _() was not being recognized when building the
    documentation while preserving the delayed translation of error
    messages.

    Closes-Bug: #1211507
    Related-Bug: #1209413

    Change-Id: I5d52941e1f08ec656f7279efb6cdf496d81861da