Don't prompt for patches when outputting lint results as XML.

Summary: The Checkstyle XML output format is not intended to be an interactive workflow.

Test Plan: Introduced linter issues and ran `arc lint`. Verified that no interactive prompt was shown.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9107
Be more strict with the type of `.arclint` properties.

Summary: Although this provides less context in terms of the error message (for example, `Parameter has invalid type. Expected type 'optional regex|list<regex>', got type 'list<string>'.`), I think that it is the right approach. I think that `PhutilTypeSpec::checkMap` should be improved such that additional context is provided in the exception message.

Test Plan: Ran `arc lint`. Modified `.arclint` to contain an invalid regex and ran `arc lint` again.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9089
Minor improvements to the `ArcanistLintCheckstyleXMLRenderer` class.

Summary: Ref T4948. Move the `startDocument` code to a `renderPreamble` function so that, at least theoretically, the renderer can be reused. Otherwise, the only way to reuse the renderer would be to construct a new instance.

Test Plan: Ran `arc lint --output xml` and verified that the output looked reasonable.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4948

Differential Revision: https://secure.phabricator.com/D9108
Merge branch 'master' of github.com:facebook/arcanist