projectClassLoader is an URLClassLoader, which implements Closeable. instanceof-check not required

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1619563 13f79535-47bb-0310-9956-ffa450edef68
Ensure that Writer is always closed

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1619564 13f79535-47bb-0310-9956-ffa450edef68
Fix Bad practice - Classloaders should only be created inside doPrivileged block

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1619571 13f79535-47bb-0310-9956-ffa450edef68