Upgrade "arc upload" to use SHA256

Summary: Fixes T12464. Moves "arc upload" to SHA256 where applicable.

Test Plan: Ran `arc upload` against a server with D17620 twice, saw it skip the actual upload the second time.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12464

Differential Revision: https://secure.phabricator.com/D17622

src/upload/ArcanistFileDataRef.php

@@ -346,11 +346,23 @@ final class ArcanistFileDataRef extends Phobject {
   }
 
   private function newFileHash($path) {
-    return null;
+    $hash = hash_file('sha256', $path, $raw_output = false);
+
+    if ($hash === false) {
+      return null;
+    }
+
+    return $hash;
   }
 
   private function newDataHash($data) {
-    return null;
+    $hash = hash('sha256', $data, $raw_output = false);
+
+    if ($hash === false) {
+      return null;
+    }
+
+    return $hash;
   }
 
 }