Ready more linters and linter functions for .arclint

Summary:
Ref T3186. Ref T2039. Continues work on readying linters for `.arclint`.

  - **Ruby**: Make this an ExternalLinter.
  - **Priority**: Currently, linters have an implicit "correct" order (notably, the "NoLint" linter needs to run before other linters). Make this explicit by introducing `getLinterPriority()`.
  - **Binaries**: Currently, linters manually reject binary files. Instead, reject binary files by default (linters can override this if they do want to lint binary files).
  - **Deleted Files**: Currently, linters manually reject deleted files (usually in engines). Instead, reject deleted files by default (linters can override this).
  - **Severity**: Move this `.arclint` config option up to top level.
  - **willLintPaths()**: This method is abstract, but almost all linters provide a trivial implementation. Provide a trivial implementation in the base class.
  - **getLintSeverityMap()/getLintNameMap()**: A bunch of linters have empty implementations; these are redundant. Remove them.
  - **Spelling**: clean up some dead / test-only / unconventional code.
  - **`.arclint`**: Allow the filename, generated, nolint, text, spelling and ruby linters to be configured via `.arclint`.

Test Plan:
https://github.com/epriestley/arclint-examples/commit/458beca3d65b64d52ed612904ae66eb837118b94

Ran unit tests.

Reviewers: btrahan

Reviewed By: btrahan

CC: Firehed, aran

Maniphest Tasks: T2039, T3186

Differential Revision: https://secure.phabricator.com/D6805
Automatically answer excuse prompts if stdin is not a TTY

Summary: Fixes T3696. Currently, we abort. If stdin is not a TTY, we should just continue. A script which cares could conceivably run `arc lint` and `arc unit` separately, but it seems unlikely that any script would ever want to fail here.

Test Plan: Ran `echo -n '' | arc diff --create --verbatim` with a lint error and got a revision (D6720).

Reviewers: Firehed, btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3696

Differential Revision: https://secure.phabricator.com/D6721
Add support for 'phpunit_binary' config setting

Summary:
If present, this will override the default phpunit path. Allows easy
integration of Composer-provided installs of phpunit (ex. set phpunit_binary to
vendor/bin/phpunit). If the path provided doesn't resolve to an executable it
will assume the path is relative to the project root.

fix line length issue

Test Plan:
Added phpunit_binary to .arcconfig in a simple project using Composer with
phpunit/phpunit package as part of require-dev (installed to
$ROOT/vendor/bin/phpunit). Phpunit not otherwise installed on the system. Set
unit.engine to PhpunitTestEngine. Confirmed that 'arc unit' used the specified
binary, both at project root and from subdirectories.

Reviewers: epriestley

CC: aurelijus, Korvin, aran

Differential Revision: https://secure.phabricator.com/D6791
When converting a file to a binary, populate the binary's data

Summary:
Currently, we prompt the user to mark non-UTF8 files as binary, but don't actually attach the data to the change when they do. This means we don't upload the data, and can't patch it later.

A simple reproduction case is to build a test file (I used one with bytes from 1..255):

  $ # Don't include \0, since Git treats that specially.
  $ ./echo_every_byte_from_1_to_255_inclusive.erl > example.txt

Then add it:

  $ git add example.txt
  $ git commit -a -m derp
  $ arc diff --only HEAD^

You'll be prompted to convert the file to binary:

  Do you want to mark this file as binary and continue? [Y/n] y

Before this patch, that would be followed by:

  Uploading 0 files...

...which is incorrect; we need to upload the new data. After this patch, this shows:

  Uploading 1 files...

...which is also incorrect, but only grammatically. Diffs created after this patch apply back cleanly with `arc patch` and restore the file properly.

Test Plan: Followed instructions above, restoring a textual binary conversion by using `arc patch`.

Reviewers: zeeg, btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6815
Merge remote-tracking branch 'upstream/master'