Allow blaming of seemingly binary files in SVN

Summary:
Fixes T2388.
We check for binarity later.

Test Plan: Blamed file with 'application/x-shellscript' MIME type.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2388

Differential Revision: https://secure.phabricator.com/D4605