Modified read-proof-id and read-proof-description to use pvs-dialog rather
than (format t ...) (read-line) in order to support GUIs
1. Changed, e.g., *pvs-buffer-hooks* to *pvs-buffer-hook* - only allowing a
   single binding at a time.
2. Added pvs-dialog to support simply asking for a string and returning it.
1. Modified with-pvs-hooks so that the hooks are visible to the main lisp process
2. Fixed the way responses are handled for json-y-or-n and json-dialog
Misc fixes
Made xmlrpc module specific to Allegro CL for now.