RFR: Handle binary patches in webrev

[Erik Helin]

Hi all,

this patch makes `git webrev` generate `.patch` files for binary files. Thanks @rwestberg for the initial reproducer!

## Testing
- [x] Added three new unit tests

Thanks,
Erik

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Commits:
 - cd9b801d: Handle binary patches in webrev

  Stats: 221 lines in 7 files changed: 185 ins; 12 del; 24 mod
Changes: https://git.openjdk.java.net/skara/pull/150/files
 Webrev: https://webrevs.openjdk.java.net/skara/150/webrev.00
  Patch: https://git.openjdk.java.net/skara/pull/150.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/150/head:pull/150

PR: https://git.openjdk.java.net/skara/pull/150