In Subversion, show "svn checkout <uri> <directory>" in Diffusion

Summary:
Ref T10923. The old behavior was to show a full command in SVN, Mercurial, and Git, like this:

• git clone <uri>
• hg clone <uri>
• svn checkout <uri> <directory>

In Git and Mercurial, the <uri> ends in something like /nice-repository-name.git so the default directory it creates is called nice-repository-name/.

In Subversion, we don't (and can't easily) do that for various reasons so we provide an explicit <directory> with the nice name.

In the update, I've changed things to just show the URI. I often found that I wanted the URI alone, not the whole clone command (for example, to fetch, remote-add, etc). This is also consistent with GitHub. Because we have nice URIs for Git and Mercurial, git clone <uri> has good behavior.

In Subversion, svn checkout <uri> has bad beahvior (you get a directory named 47/ or whatever). So continue showing the whole command there.

We can possibly tailor this after T4245 finishes up and we get access to /source/nice-repository-name/ URIs.

Test Plan:

• Viewed a Subversion repository, saw a full command.
• Viewed a Git repository, saw only a clone URI.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10923

Differential Revision: https://secure.phabricator.com/D15888