(pop-to-mark-command, push-mark-command): New commands.

(pop-to-mark-command, push-mark-command): New commands.
(set-mark-command): Use them.
Enhanced functionality when command is repeated:
- If first command set the mark (no prefix arg), repeat temporarily
enables transient-mark-mode.
- If first command jumped to mark off ring (with argument),
repeat (with or without arg) jump to next mark off ring.
- Use C-u C-u prefix to set mark after jump.
(exchange-point-and-mark): Temporarily enable transient-mark-mode
if prefix arg.