RFR: Ignore `path=` lines in git credential fill output.

[JornVernee via github.com]

Hi,

I'm trying out skara, but when running `git fork https://github.com/openjdk/panama git-panama` I'm getting the following exception:

```
Exception in thread "main" java.io.IOException: 'git credential' returned unexpected line: path=
        at org.openjdk.skara.cli/org.openjdk.skara.cli.GitCredentials.fill(GitCredentials.java:101)
        at org.openjdk.skara.cli/org.openjdk.skara.cli.GitFork.main(GitFork.java:130)
        at org.openjdk.skara.cli/org.openjdk.skara.cli.GitSkara.main(GitSkara.java:130)
```

Looks like `path=` is not handled yet?

This PR adds some handling that ignores lines starting with `path=` for now, but maybe any unknown line should be ignored instead of throwing an exception, what do you think?

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

Commits:
 - 2149adba:	Ignore `path=` lines in git credential fill output.

Pull request:
http://git.openjdk.java.net/skara/pull/7

Webrev:
https://openjdk.github.io/cr/skara/7/webrev.00

Patch:
http://git.openjdk.java.net/skara/pull/7.diff

Fetch command:
git fetch https://github.com/openjdk/skara.git 2149adba:pr/7