Restore the usage of the document fragment in XInclude processing to handle...

Restore the usage of the document fragment in XInclude processing to handle xi:include as root elements; delay the recursive expansion of includes until the document fragment has been placed in the final location [XERCESC-1918]

git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@933210 13f79535-47bb-0310-9956-ffa450edef68