SVNAdaptor from Tigris

[Tom Zeller]

> Bringing this up one more time as Rod has just checked in his code...

I was wrong about "provided", I thought Maven did not automatically
retrieve "provided" dependencies from remote repositories, it does.

So, I added SVNkit as an _optional_ dependency to the v3 parent POM
with the default "compile" scope and not "provided".

I think that satisfies the issue at hand, apologies for the noise.