We log misleading WARN log events from Log4j about message factories and unexpected formatting.
2016-05-29 18:21:46,712 main WARN The Logger com.example.foo was created with the message factory org.apache.logging.log4j.spi.MessageFactory2Adapter@46bc9802 and is now requested with the message factory org.apache.logging.log4j.m
essage.StringFormatterMessageFactory@510e0dd2, which may create log events with unexpected formatting.
This is because in 2.6, AbstractMessageFactory implements MessageFactory instead of MessageFactory2.
This issue changes AbstractMessageFactory to implement MessageFactory2.