Make arcanist lint tests flexible about testcase formatting

Summary:
We currently require an exact number of "~" characters, but this is needless and error-prone.

Instead, allow any number larger than 3.

Test Plan:
  - Added meta test-case.
  - Ran `arc unit --everything`.

Reviewers: btrahan, thoughtpolice

Reviewed By: thoughtpolice

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10251
[lint] Add HLint-based Haskell linter

Summary:
This adds a lint engine for `hlint`, which is the standard and most general Haskell lint tool around these days.

Signed-off-by: Austin Seipp <aseipp@pobox.com>

Test Plan: Install `hlint`, and run `arc unit`.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Projects: #arcanist

Differential Revision: https://secure.phabricator.com/D10250
Don't parse separator tabs as part of the filename in Git diffs which affect files with spaces

Summary:
Fixes T5870. When a filename contains spaces, Git will add a "\t" at the end of the "---" and "+++" lines. We currently consume this and think we're reading a file called "blah blah\t".

Instead, parse it out as not part of the filename.

Test Plan: Added failing unit test and made it pass.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5870

Differential Revision: https://secure.phabricator.com/D10267