Support `arc lint --output none`

Summary:
I want to run lint on background and I'm interested only in side effect of caching (and maybe exit status).
This is better than discarding stdout later because we don't do unnecessary work and error conditions are still printed.

Test Plan:
  $ arc lint --output none # with error
  $ echo $?
  $ arc lint --output none # with no lintable paths
  $ arc lint --output none # witout errors

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5106
Initialize used variable in lint console renderer
Catch exceptions in didRunLinters()

Test Plan: Threw in `didRunLinters()` of one linter, still saw the result of other linters and "Some linters failed" at the end.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5124
Include linter class MD5 in linter version

Summary:
People constantly forget to bump the linter version and I don't see a way how to stop it.
This may bump the version even if it wouldn't be required but let's rather undercache than overcache.

Test Plan: `var_dump($version)`.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5129
Fix arc lint on working copy changes in mercurial repos

Summary:
Previously, running arc lint on a set of changes that only
existed in your working copy threw an exception in mercurial repos.
It was trying to use the revset "...." (i.e. the range from . to .),
which didn't parse. Even if I fix that it still doesn't work because
getRawDiffText did not include the working copy changes (which it does
in git).  I removed the check so the function now acts the same as in
git and arc lint works on working copy changes. I've seen this error before
in other places so hopefully this change will also fix any other areas,
that depended on getRawDiffText working the same as git.

The logic I removed was added in D1954 to support diffing against
uncommited changes.  That workflow should be unchanged.  arc diff will
still prompt the user if there are uncommited changes, and the user can
still choose to abort or continue.

Let me know if I missed something important which makes this a bad idea.

Test Plan:
Edited a file in the working directory of a hg repo.
arc lint
Verified lint ran successfully.

Also ran arc diff and land with and without working copy changes to make sure
they still work.  I'd kill for some tests in this area...

Reviewers: epriestley, vrana

Reviewed By: epriestley

CC: dschleimer, bos, sid0, aran, Korvin

Maniphest Tasks: T1631

Differential Revision: https://secure.phabricator.com/D5130
Merge branch 'master' of http://github.com/facebook/arcanist