Differential defaults to 'ignore-trailing' until indentation issues are solved.

Summary:
'ignore-all' is very confusing, especially for Python, because the indentation
is incorrect.

Test Plan:
Tested loading D240353 without any options and made sure 'ignore-trailing' was
selected and the diff looked correct.

Reviewed By: aran
Reviewers: jungejason, simpkins, aran, dpepper
Commenters: dpepper
CC: grglr, aran, dpepper, tuomaspelkonen
Differential Revision: 171

src/applications/differential/view/changesetlistview/DifferentialChangesetListView.php

@@ -23,7 +23,9 @@ class DifferentialChangesetListView extends AphrontView {
   private $revision;
   private $renderURI = '/differential/changeset/';
   private $vsMap = array();
-  private $whitespace = null;
+
+  // This is the Default value for whitespace mode!
+  private $whitespace = 'ignore-trailing';
 
   public function setChangesets($changesets) {
     $this->changesets = $changesets;
@@ -51,10 +53,16 @@ class DifferentialChangesetListView extends AphrontView {
   }
 
   public function setWhitespace($whitespace) {
-    $this->whitespace = $whitespace;
+    if ($whitespace) {
+      $this->whitespace = $whitespace;
+    }
     return $this;
   }
 
+  public function getWhitespace() {
+    return $this->whitespace;
+  }
+
   public function render() {
     require_celerity_resource('differential-changeset-view-css');