Fix double file content in files in new subdirectories in Subversion

Summary:
Fixes T5555. Normally, when we `svn diff subdir/`, we use `--depth empty` to get only changes for the directory itself (usually, property changes).

However, this flag has no effect if the directory is newly added.

Adjust the diff parser so that if two sets of hunks are specified for a single file in a raw diff, we let the last one win instead of including both. This approach is a broadly more reasonable interpretation of these diffs.

Test Plan:
  - Added a new file in a new subdirectory in Subversion.
  - Ran `arc diff --only`.
  - No double file content in resulting diff.
  - Added unit test.
  - There's fairly comprehensive unit test coverage for this stuff.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5555

Differential Revision: https://secure.phabricator.com/D9921
Reformat README as Remarkup

Summary: We have Remarkup, so why not use it?

Test Plan: See D9946.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9949
Add a newline to `externals/includes/README`

Summary: For consistency, add a trailing newline to `externals/includes/README`. See D9940.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9950
Remove duplicate newline

Summary: Remove a duplicate newline from end-of-file.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9951
Add Phrequent workflows to Arcanist

Summary:
Depends on D9906.

This adds `arc start`, `arc stop` and `arc tracking` for tracking tasks, diffs and other objects in Phrequent.

Test Plan: Tested this against a local install.

Reviewers: skyronic, #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: maxhodak, hach-que, aran, epriestley, Korvin

Maniphest Tasks: T3569, T3969

Differential Revision: https://secure.phabricator.com/D7327
Remove "Stopped" logic from Phrequent workflows

Summary: We can remove this "Stopped" code as per feedback on D7327.  I think having the full text of "In Progress" and "Suspended" is much clearer than just a '*' though, so I've only removed the ongoing check.

Test Plan: Ran a combination of `arc start`, `arc stop` and `arc time` and it all worked.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9955
Use have/need data in ArcanistPhutilLibraryLinter

Summary: Ref T5640. In D9864, the data this linter pulls out of the map was changed, breaking "use of undeclared function" warnings.

Test Plan:
```
>>> Lint for src/future/FutureProxy.php:

   Error  (PHL1) Unknown Symbol
    Use of unknown function 'qqqqqq'. Common causes are:

      - Your libphutil/ is out of date.
        This is the most common cause.
        Update this copy of libphutil: /INSECURE/devtools/libphutil

      - Some other library is out of date.
        Update the library this symbol appears in.

      - This symbol is misspelled.
        Spell the symbol name correctly.
        Symbol name spelling is case-sensitive.

      - This symbol was added recently.
        Run `arc liberate` on the library it was added to.

      - This symbol is external. Use `@phutil-external-symbol`.
        Use `grep` to find usage examples of this directive.

    *** ALTHOUGH USUALLY EASY TO FIX, THIS IS A SERIOUS ERROR.
    *** THIS ERROR IS YOUR FAULT. YOU MUST RESOLVE IT.

              15       $this->setProxiedFuture($proxied);
              16     }
              17
    >>>       18     qqqqqq();
              19   }
              20
              21   public function setProxiedFuture(Future $proxied) {
```

Reviewers: joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5640

Differential Revision: https://secure.phabricator.com/D9954
Don't explicitly name abstract base classes

Summary:
Ref T5655. It is superfluous to include "base" in the name of an abstract base class. Furthermore, it is not done consistently within the code base.

In order to retain compatibility with external code, I have kept the `ArcanistBaseWorkflow` class (which trivially extends from `ArcanistWorkflow`), but it is now deprecated and should output a warning message. Similarly for `ArcanistBaseUnitTestEngine`.

Test Plan: Created a workflow which extends from `ArcanistBaseWorkflow`. Executed the workflow and saw a deprecation warning.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin, aurelijus

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D9983
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