R1:6b0138c1aeb6

prevents users from deleting already deleted/moved phriction documents

Summary:
Deps D5198 since it uses a constant from D5198

accidentalbigdiff

I sure doubled the size of this file ^^

Could be that I added unserious business.

Test Plan:
Created a page. Had it open in two browser windows. Deleted in one. This is the second attempt:

{F34458}

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5202