LOG4J2-674: Made RollingFileAppender buffer size configurable;
LOG4J2-622: RollingFileManager now correctly honours the bufferedIO configuration after rollover.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1604312 13f79535-47bb-0310-9956-ffa450edef68