RFR: 184: git-webrev exception on deleted files in hg

[Erik Helin]

Hi all,

please review this patch that improves how our Mercurial plugin detects copied
and renamed files. We have to have our `diff_git_raw` implementation produce
the same results as `hg diff --git`, otherwise one might consider a file
renamed and the other one not, resulting in problems.

This patch make the results of `diff_git_raw` produce more similar results as
`hg diff --git` by making use of the `mercurial.copies` utility.

Thanks,
Erik

- [x] `make test`
- [x] Manually creating a webrev for the patch attached to the bug

-------------

Commits:
 - 5d18de23: 184: git-webrev exception on deleted files in hg

Changes: https://git.openjdk.java.net/skara/pull/307/files
 Webrev: https://webrevs.openjdk.java.net/skara/307/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-184
  Stats: 25 lines in 1 file changed: 20 ins; 3 del; 2 mod
  Patch: https://git.openjdk.java.net/skara/pull/307.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/307/head:pull/307

PR: https://git.openjdk.java.net/skara/pull/307