Revamp of prompting code. New design supports keyword arguments to

Revamp of prompting code.  New design supports keyword arguments to
most prompting procedures, to support options in an extensible way.
The new keyword options are used to implement a general history
mechanism, like that previously implemented by repeat-complex-command
(which is now implemented using the new mechanism).

This edit has made incompatible changes to the calling conventions of
the following procedures:

prompt-for-buffer-name
prompt-for-expression
prompt-for-pathname
prompt-for-pathname*
prompt-for-string
prompt-for-completed-string
prompt-for-string-table-name
prompt-for-string-table-value