LOGBACK-909 Fix race condition in SMTPAppenderBase caused by shared MimeMessage instance.
removed unnecessary spawn of a connector thread
promoted socket connector to become a member to reduce overhead when creating socket connection
simplified socket re-connection logic
added missing unit test for re-establishing the socket connection when stream creation fails with IOException
added additional unit tests for stopping socket appender task on interrupts
removed unnecessary TODO comment
fix LOGBACK-116

Correct RollingCalendarTest. Modify time-zone offset handling.
Merge pull request #210 from arlampin/LOGBACK-909

LOGBACK-909 Fix race condition in SMTPAppenderBase
Add release note for LOGBACK-909 fix
Merge pull request #214 from SierraGolf/simplification-of-socketapender-connection-logic

simplification of SocketApender connection logic
Add release note for PR #214
Merge pull request #215 from hidekiy/fix-RollingCalendarTest

LOGBACK-116: RollingCalendarTest fails when user.timezone is not CEST