[xml] Line Numbers limited to 65535

[Ralf Junker <ralfjunker gmx de>]

One more question about line numbers in libxml: It seems that in tree.h, struct _xmlNode limits line numbers 
to 65535 only in this line:

  unsigned short line; /* line number */

Again, is this correct and intended?

If not, could it be extended to int, or would this break backward compatability?

Ralf