Hhvm Autoload Versions Save

This release supports:

• typed user attributes
• disabled refinement via is_foo() functions

3.27 adds runtime warnings for call-time-pass-by-reference; as bin/hh-autoload includes pseudomain code, the typechecker wasn't able to find these preivously.

This release fixes some type safety issues that are not permitted by hh_client in 3.27

• this release is available under the MIT license
• include filenames in parse exceptions
• handle empty files in HHVM 3.26.0

This release supports all experimental features that will be in 3.25; this includes moving fallback handling caching from a destructor to register_shutdown_function().

This release supports:

• safe_array=true and safe_vector_array=true
• enable_experimental_tc_features=no_fallback_in_namespaces (nightlies, expected in 3.25)

• remove support for definition-finder: this removes a circular dependency, and makes bootstrapping simpler. FactParse is now the only supported parser.
• if no hh_autoload.php is present, generate a skeleton one instead of erroring out.