For all the files in a diff, we generate little change indicators that

show the proportion of added/changed/removed lines. For binary files,

we'd end up trying to re-parse the diff, and then just draw an empty

circle. This looked particularly weird when the binary file was the only

thing in the diff.
This change updates this so that we generate some fake counts for binary

files, based on whether it's a new, deleted, or updated file. This

results in solid green, red, or yellow circles, rather than just an

empty space.
This also makes it so that if we don't have any raw counts for a diff,

we hide the lines-changed indicator in the change description (this

would previously say something like "Revision 4 ()")

Looked at a bunch of change descriptions for added/deleted/updated

  binary files. Saw that the "Diff" field now contained colored circles

  rather than empty spaces.
Saw that change descriptions for diffs that contained only empty files

  no longer had an empty set of parentheses after the diff revision

  number.
Looked at the diff file index and saw the same.
Ran unit tests.