Use format-prompt in read-string calls (that have default values)

Use format-prompt in read-string calls (that have default values)

* lisp/vc/vc-annotate.el (vc-annotate):
* lisp/vc/log-edit.el (log-edit-comment-search-backward)
(log-edit-comment-search-forward):
* lisp/textmodes/rst.el (rst-insert-list-new-item):
* lisp/server.el (server-force-delete):
* lisp/mpc.el (mpc):
* lisp/frame.el (set-frame-name):
* lisp/emulation/cua-rect.el (cua-sequence-rectangle):
* lisp/cedet/semantic/symref/list.el (semantic-symref-regexp):
* lisp/calendar/todo-mode.el (todo-read-time): Use `format-prompt'
in `read-string' calls that have defaults.