* If the -f flag was not specified, just signal init and exit.reboot: Default to a clean shutdown
* Since only init can handle the RB_REROOT case* If invoked as fasthalt or fastboot, behavior is unchanged.
* If not invoked as fasthalt or fastboot, make -r mutuallywe simply signal init(8),
exclusive with -fjust like shutdown(8) does, instead of taking the system down
ourselves.
* Since only init can handle the RB_REROOT case, the -r flag is not
supported in fast mode.
* Update the usage string to correctly reflect the program being run
(fast or normal; halt, boot, or nextboot) and the options available
in each case.
* Update the manual page to make the distinction between normal and
forcedfast mode clear, better explain what shutdown(8) still does that
reboot(8) does not, and add a historical note explaining what the
difference between the two used to be.
MFC after: 1 month
Relnotes: yes yes