Fix an issue in arc patch with git-svn

Summary:
We recently moved our HEAD and it caused some issues on `arc patch` with git-svn repos. The base revision is incorrect and patch will fail. Add the check in such case to make it work.
The check was there before but removed in change b202158. The reason wasn't mentioned there though.

Test Plan: Tried it on svn.

Reviewers: lifeihuang, JoelB, #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8717
Arcanist - allow amending revisions by other authors in the working copy

Summary: Fixes T4670. Give the user an option to abort but otherwise proceed.

Test Plan: arc patch D8685 (by epriestley); arc amend

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4670

Differential Revision: https://secure.phabricator.com/D8716
Changed checking for a closed task in `arc tasks` to look for the isClosed property instead of a non-empty status

Summary: I changed the way `arc tasks` was checking to see if a maniphest task was closed from looking for a non-empty status to looking for the isClosed property submitted in D8731.

Test Plan: Run `arc tasks` and check that the tasks show open/closed correctly.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8732
Merge branch 'master' of http://github.com/facebook/arcanist