Create MavenXpp3Reader only once per methodcall
Close FileReader at end

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1483087 13f79535-47bb-0310-9956-ffa450edef68
remove used imports

git-svn-id: https://svn.apache.org/repos/asf/maven/shared/trunk@1483090 13f79535-47bb-0310-9956-ffa450edef68