PHPUnit => hacktest + fbexpect improvements

• don't attempt to rewrite non-PHPUnit methods that have the same name as assertions to fbexpect - e.g. $type_spec->assertType('foo') is not a PHPUnit assertion
• handle unqualified references to PHPUnit_Framework_TestCase as a base class
• fix return types for migrated setup/teardown functions (they should be Awaitable<void>)