Remove some overly-specific dependencies
We don't appear to need this
Add composer.lock
Use abstract class properly
Make vars protected
Extract ObjectCacheInterface
Add setKeyPrefix to interface
Only check if APC is enabled once
Just access the backend directly
Don't use the full namespace
APCu appears to use 'key' instead of 'info'
Make success code a little more terse
Use memcached's own key prefix functionality
Allow changing the current time in ArrayBackend for testing
Add more coverage in ObjectCacheTest