Basic task dependencies for Maniphest

Summary:
This allows you to edit dependencies. It is a better patch than it used to be.
It depends on D725.

  - If you create a cycle, it just throws an exception and aborts the workflow.
It should not do this.
  - Tasks which depend on the current task aren't shown in the UI. Need to add a
new table for this.
  - Transaction text says "attached Task" but should probably say "added a
dependency on task".

Test Plan: Created valid and invalid dependencies between tasks. Created valid
and invalid dependencies between revisions.
Reviewed By: tuomaspelkonen
Reviewers: davidreuss, jungejason, tuomaspelkonen, aran
Commenters: codeblock
CC: aran, codeblock, tuomaspelkonen, epriestley
Differential Revision: 595

src/applications/differential/controller/revisionview/DifferentialRevisionViewController.php

@@ -440,6 +440,16 @@ class DifferentialRevisionViewController extends DifferentialController {
 
     $properties['Unit'] = $ustar.' '.$umsg.$utail;
 
+    $drevs = $revision->getAttachedPHIDs(
+      PhabricatorPHIDConstants::PHID_TYPE_DREV);
+    if ($drevs) {
+      $links = array();
+      foreach ($drevs as $drev_phid) {
+        $links[] = $handles[$drev_phid]->renderLink();
+      }
+      $properties['Depends On'] = implode('<br />', $links);
+    }
+
     if (PhabricatorEnv::getEnvConfig('maniphest.enabled')) {
       $tasks = $revision->getAttachedPHIDs(
         PhabricatorPHIDConstants::PHID_TYPE_TASK);
@@ -513,6 +523,13 @@ class DifferentialRevisionViewController extends DifferentialController {
     require_celerity_resource('phabricator-object-selector-css');
     require_celerity_resource('javelin-behavior-phabricator-object-selector');
 
+    $links[] = array(
+      'class' => 'action-dependencies',
+      'name'  => 'Edit Dependencies',
+      'href'  => "/search/attach/{$revision_phid}/DREV/dependencies/",
+      'sigil' => 'workflow',
+    );
+
     if (PhabricatorEnv::getEnvConfig('maniphest.enabled')) {
       $links[] = array(
         'class' => 'attach-maniphest',