We attempt to keep unmodified changes out of the diff viewer when

viewing interdiffs. To do this, we compare the deleted flags and also

the diff contents. However, if the diff content simply has a small

change, like a difference in timestamps in the headers, this check will

fail and the otherwise unmodified file will be shown.
Now, when we generate diffs, we calculate SHAs and store them in the

file's extra_data. We can use these to compare the SHAs of patched files

to see if there will be any changes to show.

Loaded an interdiff containing some files that should't have been shown.

Saw the files, but then I reloaded and the files were no longer shown

(since the SHAs were calculated at that point and were properly compared).