Perform case-insensitive check for PHPUnit test finder to not return original file

Summary: PhpunitTestEngine incorrectly included some source files as tests when run on a case-insensive fiesystem. This fixes that behavior. It could introduce problems for case-sensive users, but it's extremely unlikely to be an issue in practice (who would put a file in both Tests/ and tests/ and expect different results for the two?)

Test Plan: arc unit before and after change on OS X. Stubs and autoloaders in .../tests/... directories are no longer picked up.

Reviewers: epriestley

Reviewed By: epriestley

CC: aurelijus, Korvin, aran

Differential Revision: https://secure.phabricator.com/D7048
Prevent detailed code coverage from accessing missing report.

Summary:
Fixes T3856.

Detailed code coverage iterates over all of the files with changes in the current repository, however the code coverage tool might not generate a report for all changed files in the repository, and this would result in an undefined index error.

As an additional bonus, since changes to binary files won't be reported by code coverage tools, this also prevents binary data from being outputted to the console.

Test Plan:
Change a binary file in a repository and run a code coverage tool.  The binary file should be reported as 0% code coverage, but the file contents should not be rendered to the console.

Change a code file that is not covered by a code coverage tool and run code coverage.  The file should be reported as 0% code coverage, and the file contents should not be displayed.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T3856

Differential Revision: https://secure.phabricator.com/D7051
Add C# tools and xUnit unit test engines.

Summary:
This implements Arcanist support for the xUnit testing framework.  It also supports code coverage by way of `cstools` (which is something I've written).

The unit test support works under both Linux and Windows, while the code coverage support has only been tested under Linux (one would assume it would also work under Windows given that Windows has a super-set of functionality in the C# world).

The Arcanist support assumes that the directory layout will be something like:

  * MyProject
  * MyProject.Tests

When files are changed in either MyProject or MyProject.Tests, it causes MyProject.Tests to be built and the xUnit runner to be executed on the resulting binary.

Test Plan: I guess if really wanted to, you could create a C# project in MonoDevelop, set up `.arcconfig` to point to this unit test engine, and download and build xUnit and cstools.  Run `arc unit --coverage` to see the results of your unit test coverage.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T3859

Differential Revision: https://secure.phabricator.com/D7058
Fix an issue where method prototypes have different signatures

Summary: PHP whines about this:

> [2013-09-23 08:09:22] ERROR 2048: Declaration of CSharpToolsTestEngine::loadEnvironment() should be compatible with XUnitTestEngine::loadEnvironment($config_item = 'unit.xunit...') at [/INSECURE/devtools/arcanist/src/unit/engine/CSharpToolsTestEngine.php:13]

Auditors: jamesr, btrahan
Merge branch 'master' of http://github.com/facebook/arcanist