LOG4NET-408 InterprocessLock forgot there was a Mutex to close after closing the file for the first time, causing problems with rolling files.  Patch by  Igor Candido via github PR.  closes #6

git-svn-id: https://svn.apache.org/repos/asf/logging/log4net/trunk@1544744 13f79535-47bb-0310-9956-ffa450edef68