Fix dynamic string usage as safe input

Test Plan: Copied the code in a script, changed `phutil_passthru()` to `echo csprintf()` and ran it.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4805
Allow `arc diff` and similar to run on systems with no `git`

Summary:
We assume `git` is available now, but should not. Specifically, if a user runs a working copy operation like `arc list` in an SVN working copy without `git` available, they get this error: P707

We interpret git errors very narrowly; be more liberal in how we interpret them. This assumes users working with `git` will have a functional `git`, but this seems like a reasonable assumption and lets us remove some error text matching code.

Test Plan: Changed `git` to `girt`, ran `arc list`, saw a reasonable exception. Changed back to `git`, saw git detected.

Reviewers: btrahan, vrana

Reviewed By: vrana

CC: svemir, aran

Differential Revision: https://secure.phabricator.com/D4804
Implement hook for checking switch lint

Summary:
We want to use it for `yield` and `invariant_violation()` which throws.
Having node instead of token would be better but this would be enough.

Test Plan: Implemented a hook in FB repo and added a test case there.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4821
Record commit email information from `arc`

Summary:
Record author email information in `arc diff`, so we can recreate it in `arc patch` and elsewhere without creating any kind of email exposure issues.

In Mercurial, we currently store the whole string ("username <email@domain.com>"). Make this consistent with Git.

Test Plan: Created git and hg diffs, saw authorEmail populated.

Reviewers: btrahan, edward, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4825
Make "arc patch" read `authorName` and `authorEmail`

Summary: If provided, have `arc patch` use `authorName` / `authorEmail`. This simplifies handling and makes patches more portable between version control systems (previously, information was generated in the diff's VCS, regardless of which VCS it was being applied to).

Test Plan: Created a diff with author `derp <derp@derp.com>`, ran `arc patch --diff x`, got a local commit with that author.

Reviewers: btrahan, edward, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D4827
Merge branch 'master' of http://github.com/facebook/arcanist