Use an abstract method to create the SyslogOutputStream that subclasses can override
LOGBACK-268 - Fair locking in OutputStreamAppender

Fix LOGBACK-268 by using a fair ReentrantLock (instead of object
synchronization).
Merge pull request #178 from pkwarren/fair_locking_appender

LOGBACK-268 - Fair locking in OutputStreamAppender
Updating release notes for LOGBACK-890
Merge pull request #180 from mveitas/master

Use an abstract method to create the SyslogOutputStream that subclasses can override