Pass the file contents instead of the file path to `phutil_json_decode`.

Summary: See D9681#22.

Test Plan: Created an empty `.git/arc/config` file... no exception was thrown.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9704
Fix a spelling mistake and tidy up whitespace

Summary: Self-explanatory.

Test Plan: Eye-ball it.

Reviewers: epriestley, chad, #blessed_reviewers

Reviewed By: chad, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9705
`ArcanistChmodLinter` should not allow certain MIME types to be executable

Summary: Fixes T5466. An image is an example of a binary which should //not// be executable. Modify the `ArcanistChmodLinter` to disallow certain blacklisted MIME types from being executable.

Test Plan: Created an executable image file and ran `arc lint` over this file.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: richardvanvelzen, epriestley, Korvin

Maniphest Tasks: T5466

Differential Revision: https://secure.phabricator.com/D9723
Patch: don't complain about reviewers not being specified.
This will break in the future when upstream arc incorporates T4631. Hopefully there will be a better solution by then