Note that our usage of `$asSingleton` in `get()` is fine. Quote from the PSR:
> Two successive calls to get with the same identifier SHOULD return the same value. However, depending on the implementor design and/or user configuration, different values might be returned, so user SHOULD NOT rely on getting the same value on 2 successive calls.
API Remove Director::$test_servers / $dev_servers
API Remove MODULES_PATH / MODULES_DIR constants
ENHANCEMENT Injector backtick syntax now supports environment variables as well as constants
Fixes#6588
API Implement enhanced pluralisation
Remove Zend_Translate and all Zend dependencies from i18n
Deprecated $context from i18n::_t()
Warn on missing default string for i18n::_t()
