Better error message when a change is not found

[Ovid]

I recently tried to deploy on a shared server and encountered this error:

$ sqitch deploy some_project
Cannot find 3aa4c0d2abbdffd6552c5ec504ab51d22a5aea21 in the plan

The status command gave this:

$ sqitch status some_project;
# On database some_project
# Project:  corp-some_project
# Change:   3aa4c0d2abbdffd6552c5ec504ab51d22a5aea21
# Name:     some-index-to-a-table
# Deployed: 2014-12-10 19:51:36 -0800
# By:       Colin Olleague <c.olleague@example.com>
#
Cannot find this change in sqitch/sqitch.plan
Make sure you are connected to the proper database for this project.

After a lot of debugging, I found out that "Colin" has deployed, but accidentally reverted his plan changes. So he went in and manually added them to sqitch.plan. The date, email, and note were all different from what was in the sqitch.changes table, so the SHA1 didn't match. Since the sqitch.changes.change value matched what was in the sqitch.plan file, it would be great if the error message could point out that a potentially identical plan is in the sqitch.plan file, but with a different checksum. It would have made debugging easier (I saw the change in the plan, but I had no idea that it had been manually edited, thus causing quite a bit of digging through code).

[theory]

Have a look at Engine.pm and feel free to suggest a change. You would likely need to call latest_change() to get information about the change represented by $id and include it in the message.