Fixed whitespace options in Differential.

Summary:
Whitespace options could not be selected and the 'ignore_all' was not working.

Test Plan:
Made sure that whitespace is ignored correctly and selected option is handled
correctly.

Reviewed By: jungejason
Reviewers: jungejason
CC: epriestley, jungejason, tuomaspelkonen
Differential Revision: 149

src/applications/differential/parser/changeset/DifferentialChangesetParser.php

@@ -675,10 +675,10 @@ EOSYNTHETIC;
 
           $diff = DifferentialDiff::newFromRawChanges($changes);
           $changesets = $diff->getChangesets();
-          $alt_changeset = reset($changesets);
+          $changeset = reset($changesets);
 
           $this->subparser = new DifferentialChangesetParser();
-          $this->subparser->setChangeset($alt_changeset);
+          $this->subparser->setChangeset($changeset);
           $this->subparser->setWhitespaceMode(self::WHITESPACE_IGNORE_TRAILING);
         }
         foreach ($changeset->getHunks() as $hunk) {