RFR: vcs: lower rename detection to 90%

[Erik Helin]

Hi all,

please review this small patch that lowers rename and copy detection for `GitRepository` to `90%`. The default value of
`50%` is too small for most OpenJDK patches given that the copyright + license header can easily be 19 lines. `99%`
turned out to be a bit too strict for generating good looking webrevs, so lets take it down to `90%` and see how it
goes.

Testing:
- [x] `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - vcs: lower rename detection to 90%

Changes: https://git.openjdk.java.net/skara/pull/714/files
 Webrev: https://webrevs.openjdk.java.net/skara/714/webrev.00
  Stats: 6 lines in 2 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/skara/pull/714.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/714/head:pull/714

PR: https://git.openjdk.java.net/skara/pull/714