Hhvm Autoload Versions Save

• list allowed FIXME codes in .hhconfig (required since HHVM 4.62)
• migrate array type annotations to varray or darray (required since HHVM 4.68)

Prior releases will unregister any SPL autoloaders; this behavior was added a time when it was normal for Composer's PHP autoloader to be registered first. Removing as:

• Composer's PHP autoloader has not been usable in HHVM for some time
• The SPL autoload mechanism has been removed from current nightly builds of HHVM; attempting to unregister SPL autoloaders is now a type error

We supported autoload declarations in composer.json files for compatibility with PHP projects, but most PHP files can no longer be parsed by HHVM, so this support is no longer useful and usually results in parsing errors.

Any Hack projects that relied on autoload declarations in their composer.json files will now have to provide a hh_autoload.json file instead.

Fixes multiple issues where we relied on deprecated or no longer supported HHVM features.

No longer depends on the error_php_lambdas setting being turned off, so it can now be used from projects with stricter settings without causing Hack errors.

No longer depends on the disallow_silence setting being turned off, so it can now be used from projects with stricter settings without causing Hack errors.

• hhvm-autoload supports using hh_client to find definitions from the autoload map; this is intended for development environments. This was broken under HHVM 4.20
• add an HH_FORCE_IS_DEV environment variable to force the return value of \Facebook\AutoloadMap\Generated\is_dev(); this is intended for unit testing functionality that has different default behavior in prod vs dev