Properly normalize Perforce diffs with unchanged, moved files.

This was part of my original change, but got left out in the version
that was pushed upstream.

PerforceTool.normalize_patch looks to see if the diff being processed
represents an unmoved, changed file. The header we use for this isn't an
actual diff, and will make patch upset, so we normalize it to a blank
patch.
Fix timezone warnings when running search index command.

If the database has time fields which are un-annotated with a time zone, the
index management command will spew a bunch of warnings. If people have this
running via crontab, they'll get an email with all of that.

Fixes issue 2830.
Reviewed at http://reviews.reviewboard.org/r/3742/