Make Phabricator clone bare git repositories

Summary:
This doesn't really impact anything very much, but is a little cleaner than cloning repositories with a working copy. It's somewhat important for allowing pushes, because you can't push to a checked-out branch.

Mercurial has a similar option (`--noupdate`) but leave that alone for now.

The origin stuff was mostly for sanity/explicitness purposes -- I believe it's safe to remove in all non-ridiculous cases. Git fails with it in bare repositories (it automatically creates an `origin`, but doesn't create the local refs for it, or something).

Test Plan: Nuked a repo, re-cloned it, pulled and updated it several times. Browsed both bare and non-bare repos in Diffusion.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2230

Differential Revision: https://secure.phabricator.com/D7430

src/applications/diffusion/controller/DiffusionRepositoryController.php

@@ -40,6 +40,7 @@ final class DiffusionRepositoryController extends DiffusionController {
           }
         }
       }
+      $history_exception = null;
     } catch (Exception $ex) {
       $history_results = null;
       $history = null;
@@ -68,6 +69,7 @@ final class DiffusionRepositoryController extends DiffusionController {
         }
       }
 
+      $browse_exception = null;
     } catch (Exception $ex) {
       $browse_results = null;
       $browse_paths = null;