Accept GET requests for jump nav

Summary:
The URL /jump/?jump=%s now does the same thing as the POST version,
except that if it couldn't jump to anything, it loads /jump/ with the
query filled in so you can just press enter (we don't save searches
without a CSRF token).

(hsb: Sorry for stealing your task! It hadn't been updated in two months
so I figured you were likely not actively working on it.)

Test Plan:
Loaded given URL with different queries (including various
flavors of nothing). Search worked as expected.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1036

Differential Revision: https://secure.phabricator.com/D3047

src/applications/directory/controller/PhabricatorDirectoryMainController.php

@@ -105,13 +105,12 @@ final class PhabricatorDirectoryMainController
   private function buildJumpResponse($nav) {
     $request = $this->getRequest();
 
-    if ($request->isFormPost()) {
     $jump = $request->getStr('jump');
 
     $response = PhabricatorJumpNavHandler::jumpPostResponse($jump);
     if ($response) {
       return $response;
-      } else {
+    } else if ($request->isFormPost()) {
       $query = new PhabricatorSearchQuery();
       $query->setQuery($jump);
       $query->save();
@@ -119,10 +118,9 @@ final class PhabricatorDirectoryMainController
       return id(new AphrontRedirectResponse())
         ->setURI('/search/'.$query->getQueryKey().'/');
     }
-    }
 
 
-    $nav->appendChild($this->buildJumpPanel());
+    $nav->appendChild($this->buildJumpPanel($jump));
     return $this->buildStandardPageResponse(
       $nav,
       array(
@@ -430,7 +428,7 @@ final class PhabricatorDirectoryMainController
       '</div>';
   }
 
-  private function buildJumpPanel() {
+  private function buildJumpPanel($query=null) {
     $request = $this->getRequest();
     $user = $request->getUser();
 
@@ -459,6 +457,7 @@ final class PhabricatorDirectoryMainController
         'class' => 'phabricator-jump-nav',
         'name'  => 'jump',
         'id'    => $uniq_id,
+        'value' => $query,
       ));
     $jump_caption = phutil_render_tag(
       'p',