[JENKINS-26318] Migrate to svnkit 1.8

[christ66]

This pull request does two things:

• Migrate to use the default svnkit library.
• Use the latest svnkit 1.8 library.

This will make the BlameSubversion-plugin compatible with the latest subversion plugin, and fix JENKINS-26318

@reviewbybees

[ghost]

This pull request originates from a CloudBees employee. At CloudBees, we require that all pull requests be reviewed by other CloudBees employees before we seek to have the change accepted. If you want to learn more about our process please see this explanation.

[tfennelly]

Would it not be better to name this something else so as not to cause confusion between it and org.tmatesoft.svn.core.auth.ISVNAuthenticationManager?

[tfennelly]

🐝

But two things:

1. In general, I would not be a big fan of knowingly creating classes with the same names as existing classes (SVNSSLAuthentication etc in this case).
2. I'd say others would not like the fact that new code was added below the hudson package.