#376 XenaInputSource from InputStream does not work as expected

[Terry O'Neill]

A XenaInputSource can currently be created from an InputStream, however when this is done functionality such as normalise does not work as expected. There are other areas that assume that the XenaInputSource represents a file and areas that assume that the XenaInputSource can be read and re-read repeatedly. The code should be changed so that it will work when using a XenaInputSource from any sort of InputStream.