Improve `arc land` recovery from issues with the remote.

Summary:
Fixes T2138.

  - When a pull fails, restore the original branch.
  - When a push fails, complain about it really loudly.

NOTE: No test plan for push yet since I'm not sure this is the right remedy, see T2138 for discsusion.

Test Plan:
  - Tested pull by changing "git pull" to "git xxpull" and running "arc land". Saw the pull fail and my original branch restored.

Reviewers: vrana, aran

Reviewed By: vrana

Maniphest Tasks: T2138

Differential Revision: https://secure.phabricator.com/D4265
Add a flake8 linter

Summary: flake8 is the better maintained combination of pep8 and pyflakes

Test Plan: There's a test!

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin, jack

Differential Revision: https://secure.phabricator.com/D4082
Correct description and severity on Flake8 linter

Test Plan: do it live

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4274
Correct spelling for "arc" commands

Summary:
I type "arc brnach" about 300 times per day.

  - Allow arc commands to be specified by unique prefix ("exp" for "export", "lib" for "liberate").
  - Allow arc commands to be specified by unique levenshtein edit distance <= 2 ("brnach" for "branch", "halp" for "help", "ptach" for "patch").
  - Reorganize code out of "arcanist.php".

I think this will be uncontentious because arc commands are rarely destructive, but if people complain we can either require certain commands be typed exactly (maybe "land"?) or allow this feature to be disabled in configuration.

Test Plan:
  $ arc br
  Usage Exception: Unknown command 'br'. Try 'arc help'.

  Did you mean:
      branch
      browse

  $ arc brnachh
  Usage Exception: Unknown command 'brnachh'. Try 'arc help'.
  $ arc brnach
  (Assuming 'brnach' is the British spelling of 'branch'.)
     doc-security        No Revision      security
     sms                 Needs Revision   D319: Add SMS support to Phabricator
     phxtag              No Revision      derp
     arantag             No Revision      derp
  ...

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4305
make arc install-certificate <uri> work if uri is specified

Summary: see title

Test Plan: ran arc install-certificate <uri> in a directory without an .arcconfig and it worked! ran arc install-certificate in a directory with an .arcconfig and it worked! ran arc install-certificate <uri> in a directory with an .arcconfig and noted it correctly overrode the .arcconfig

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2251

Differential Revision: https://secure.phabricator.com/D4332
Add cpplint.py engine

Summary: Adds arc lint support for cpp files with Google's cpplint.py lint checking.

Test Plan: ran it on some cpp files. Added unit tests

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4344
CppCheck linter

Summary:
Lints cpp code using the cppcheck static linter.  This linter needs to
be downloaded and built from http://cppcheck.sourceforge.net/

Test Plan: Used it on a few files.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4353
Limit `arc branch` to 16 concurrent processes

Summary:
Currently, this spawns 125 concurrent processes on my machine, which overflows some limit and gives me an error:

  PHP Warning:  proc_open(): unable to create pipe Too many open files in /INSECURE/devtools/libphutil/src/future/exec/ExecFuture.php on line 491

Instead, limit parallelism to 16. The runtime is approximately the same for me, and dominated by other concerns (conduit calls).

Test Plan: Ran `arc branch` successfully. Ran `arc branch --trace`, observed behavior.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4336
Fix cppcheck path finding

Summary: This fix lets you run arc lint from any directory in the repository

Test Plan: Ran arc lint from any directory

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4356
Pass the constructed message to the TYPE_DIFF_DIDBUILDMESSAGE event.

Summary: We want to use TYPE_DIFF_DIDBUILDMESSAGE to abort arc diff when a message doesn't fit some

Test Plan: Created an EventListener subscribed to TYPE_DIFF_DIDBUILDMESSAGE, validated the 'message' field was filled in

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D4361
Add a comma.

Summary: Add a comma because it was going to annoy the crap out of me.

Test Plan: See the comma. :)

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4365
Fix "empty diff" error in arcanist

Summary: Ref T2296. This error is unreachable right now -- when I fixed all the "\r\n" stuff, we always end up with a nonempty first line for an empty input. Do this test earlier and more explicitly. This results in a less useful error: "expected (some junk) on line 1" instead of "can't parse an empty diff".

Test Plan: Tried to parse an empty diff, got a "you can't parse an empty diff" error.

Reviewers: btrahan, vrana, codeblock

Reviewed By: codeblock

CC: aran

Maniphest Tasks: T2296

Differential Revision: https://secure.phabricator.com/D4370
Fix `arc diff x y` in SVN

Summary:
D4186 added an "svn status --xml x y" form to getSVNStatus(), but the parser doesn't work for multiple files, since we get multiple <target /> elements in the XML output. So, curently, `arc diff` works (one target, all files) and `arc diff x` works (one target, x) but `arc diff x y` does not (more than one target, hits the exception).

  $ arc diff QUACK2 QUACK3
  Exception
  Expected exactly one XML status target.

Test Plan: Ran `arc diff QUACK2 QUACK3` in a working copy with modified QUACK2, QUACK3. Ran `arc diff`; `arc diff QUACK2`.

Reviewers: vrana, btrahan, codeblock, JThramer

Reviewed By: codeblock

CC: aran

Differential Revision: https://secure.phabricator.com/D4372
Allow `arc.bat` to work from paths with spaces in them

Summary: If you dump `arcanist/` into "Program Files" or similar, the `.bat` currently breaks. Quote the path so it doesn't. Fixes T1436.

Test Plan: Ran `arc` with `arcanist/` in a path with spaces in it.

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1436

Differential Revision: https://secure.phabricator.com/D4375
Normalize Windows directory separators in SVN

Summary: Fixes T1946.

Test Plan: Ran `arc diff --only` with added paths inside directories. Saw only "/" entries in the diff.

Reviewers: btrahan, vrana

Reviewed By: vrana

CC: aran, mbishopim3

Maniphest Tasks: T1946

Differential Revision: https://secure.phabricator.com/D4374
Fix checking for flake8 path

Test Plan:
  $ arc unit # without flake8 in path

Reviewers: zeeg

Reviewed By: zeeg

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D4379
Generate Git patches with "\n" metadata line endings unconditionally

Summary:
Fixes T2175. Git generates patches which have "\n" line endings on every system. We currently generate patches with system-dependent line endings.

Git accepts system-dependent line endings in almost call cases, but part of the parser tests for "\n" explicitly. T2175 has an example of this.

Test Plan:
Ran `arc export --git --revision D4366 > export.git` on a Windows machine, verified "\n" line endings. Ran the same with `--unified`, verified "\r\n" line endings.

(I didn't add any unit tests for this because it's Windows-dependent and very difficult to test meaningfully right now -- i.e., test that appliable patches are generated -- since the git reconstitution test doesn't run on Windows either, because we can't yet untar things there.)

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2175

Differential Revision: https://secure.phabricator.com/D4373
Run all willLintPaths() before any lintPath()

Summary:
FB runs some linters on background and it's a magnificent hack using `ParallelLinter` (two instances), `BackgroundLinter` and `FutureLinter`.
I want to simplify this by resolving the futures in engine instead of in some virtual linter.
It also seems like a better place to do it.
It should also fix caching problems I have with them (because the virtual linters don't know about the cache at all).

Test Plan: None yet.

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4380
Add some new misspellings of "hierarchy"

Summary: turns out people really like misspelling "hierarchy"

Test Plan: hope
Fix checking for lint binary paths

Summary: Like D4379.

Test Plan:
  $ arc unit

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4391