Add support for new compile time options defined in prefix file. These

control the selection of the msgloader, transcoder, and netaccessor.
Add a tiny bit of robustness to the nasty panic method.


git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@172377 13f79535-47bb-0310-9956-ffa450edef68