Imports: Add reporting of new and removed files

Imports: Add reporting of new and removed files

Make the commit message produced by import-external-git.pl also report
which files the script added and removed. Whilst this information is
available from the patch itself, having it in the commit message makes
it much easier to tell what happened when reviewing history through
git log.

Change-Id: I59e7deb0f4f1e8c22d07222e1789c66c65612992
Reviewed-on: http://gerrit.openafs.org/3334
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>