minor abnf change

["Lindelsee, Mike " <mlindels@visa.com>]

All,

We don't have to make this change, but I noticed a while back that our
xri-unreserved production is exactly the same as the iunreserved
production in IRI.  I think that we should drop xri-unreserved and just
use iunreserved directly.  Since this doesn't change the syntax at all,
it
won't affect implementations.  Does anyone have any objections to making
the change in the ABNF?

Mike