Added parameter http://apache.org/xml/features/pretty-print/space-first-level-elements to DOMLSSerializer to let the user control whether the children of the document root should have an extra line feed between them (jira# 1561)

git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@413647 13f79535-47bb-0310-9956-ffa450edef68