make the XML writers use the Uint64 header type by default
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
Users are starting to hit the size limit of the XML writers when using the UInt32 header type, which is the default. The default should be changed to UInt64 header type. Note that the UInt64 header type was introduced about 18 months ago and isn't backwards compatible. I also am going to hide the header type option for the XML writers so there is one less option for the user to worry about.