Move point to location stored in a register.
If the register contains a file name, find that file.
(To put a file name in a register, you must use `set-register'.)
If the register contains a window configuration (one frame) or a frame
configuration (all frames), restore that frame or all frames accordingly.
First argument is a character, naming the register.
Optional second arg non-nil (interactively, prefix argument) says to
delete any existing frames that the frame configuration doesn't mention.
(Otherwise, these frames are iconified.)