Implementation of Murray's proposal

Folks,

As actioned, I've made an attempt to implement Murray's proposal for
using subelements to identify the bindings for input and output ports.

I decided to use the element names 'pipe', 'document', and 'inline'
to represent the three possible kinds of bindings.

  http://www.w3.org/XML/XProc/docs/alternate/

I've also provided a diff-marked version, but the bulk of the changes
occur in sections 4.1.2, 4.2.4.3, and 4.2.9.

In particular, the discussion of assigning values to parameters
(4.2.4.3) and p:choose/p:when (4.2.9) may have changed in ways not
explicitly anticipated by the proposal.

                                        Be seeing you,
                                          norm

-- 
Norman Walsh
XML Standards Architect
Sun Microsystems, Inc.