Support SVN pre-commit hoooks

Summary:
Ref T4189. This adds SVN support, which was a little more messy than I though. Principally, we can not use `PHABRICATOR_USER` for Subversion, because it strips away the entire environment for "security reasons".

Instead, use `--tunnel-user` plus `svnlook author` to figure out the author.

Also fix "ssh://" clone URIs, which needs to be "svn+ssh://".

Test Plan:
  - Made SVN commits through the hook.
  - Made Git commits, too, to make sure I didn't break anything.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4189

Differential Revision: https://secure.phabricator.com/D7683

src/applications/diffusion/ssh/DiffusionSSHSubversionServeWorkflow.php

@@ -38,7 +38,9 @@ final class DiffusionSSHSubversionServeWorkflow
       throw new Exception("Expected `svnserve -t`!");
     }
 
-    $command = csprintf('svnserve -t');
+    $command = csprintf(
+      'svnserve -t --tunnel-user=%s',
+      $this->getUser()->getUsername());
     $command = PhabricatorDaemon::sudoCommandAsDaemonUser($command);
 
     $future = new ExecFuture('%C', $command);