Final tweaks to URI #xpointer and to XPath Transform

Hello all,

As Merlin suggested, I changed the full xpointer URI for selecting the whole
document including comments to #xpointer(/), which also required that I add
a line explaining that the root node should be expanded to its children.

I also tweaked the here() function to address concerns raised by Kent Tamura
and I, as well as to make it easier to implement.

Finally I added the warning to the XPath transform about matching text
separated by comment nodes even when those comments were excluded from the
input node-set.

The changes are marked in orange.

It was not necessary to make comments about a non-node-set return for the
XPath transform since its new construction no longer allows this to occur
(yet another reason to prefer the new design!).

I did not attempt to make any changes to account for the Limitations stated
in the latest C14N draft (which is in Joseph's hands at the moment and
should be released to the group next week).  The limitations are neither
many nor drastic, but should result in requirements on dsig implementation
developers.

Thanks,
John Boyer