Use binary safe diff in arc diff

Summary: Otherwise svn diff fails when the file is binary but the "svn:mime-type = application/x-shellscript" is missing in it.

Test Plan: arc diff succeeded against deleting a binary file which doesn't have svn:mime-type = application/x-shellscript.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D2915

scripts/repository/binary_safe_diff.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+diff "$@"
+if [ "$?" = "2" ]; then
+  exit 1
+fi

src/repository/api/ArcanistSubversionAPI.php

@@ -268,9 +268,12 @@ public function buildDiffFuture($path) {
     // itself (such as property changes) and also give us changes to any
     // files within the directory (basically, implicit recursion). We don't
     // want that, so prevent recursive diffing.
+    $root = phutil_get_library_root('arcanist');
+
     return new ExecFuture(
-      '(cd %s; svn diff --depth empty --diff-cmd diff -x -U%d %s)',
+      '(cd %s; svn diff --depth empty --diff-cmd %s -x -U%d %s)',
       $this->getPath(),
+      $root.'/../scripts/repository/binary_safe_diff.sh',
       $this->getDiffLinesOfContext(),
       $path);
   }