Enhance notifications for ticket summary changes

[ocean90]

Example: ​https://core.trac.wordpress.org/ticket/34521#comment:6

In Slack: ​https://wordpress.slack.com/archives/core-firehose/p1446291484001992

The mail:

MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
From: "WordPress Trac" <noreply@wordpress.org>
X-Trac-Version: 1.0.1
Precedence: bulk
Cc: wp-trac@lists.wordpress.org
Auto-Submitted: auto-generated
X-Mailer: Trac 1.0.1, by Edgewall Software
X-Trac-Project: WordPress Trac
Date: Sat, 31 Oct 2015 11:38:03 -0000
Reply-To: wp-hackers@lists.automattic.com
X-URL: https://core.trac.wordpress.org/
Subject: Re: [WordPress Trac] #34521: Unifying permission error messages
 (was: Translation strings - "You are not allowed to ...")
X-Trac-Ticket-URL: https://core.trac.wordpress.org/ticket/34521#comment:6
Message-ID: <064.6f4e05fa1c3b45317964e20f3fc8beb7@wordpress.org>
References: <049.7d0af072dc52a1daf46c30a6f1e989a7@wordpress.org>
X-Trac-Ticket-ID: 34521
In-Reply-To: <049.7d0af072dc52a1daf46c30a6f1e989a7@wordpress.org>

#34521: Unifying permission error messages
-----------------------------------+------------------------------
 Reporter:  ramiy                  |       Owner:
     Type:  defect (bug)           |      Status:  new
 Priority:  normal                 |   Milestone:  Awaiting Review
Component:  Text Changes           |     Version:
 Severity:  normal                 |  Resolution:
 Keywords:  has-patch 2nd-opinion  |     Focuses:
-----------------------------------+------------------------------

--
Ticket URL: <https://core.trac.wordpress.org/ticket/34521#comment:6>
WordPress Trac <https://core.trac.wordpress.org/>
WordPress publishing platform

Sadly the body doesn't contain a "Changes (by X)" line so we only have the "Subject:" line from the header.

[ocean90]

In 3086:

Slack: Avoid two PHP notices when the Trac email doesn't contain a (Comment|Changes|Description changed) line.

See #1368.

[ocean90]

In 3087:

Slack: Improve notifications for ticket summary changes.

• Parse the subject of a Trac mail because it's the only place where summary changes are mentioned.
• Include ticket summary changes in the "changes" section.
• Fall back to "Someone" if the author property isn't set. That's the case for summary only changes.

Fixes #1368.