HEADS UP: powerpc64 kernel format change

[Nathan Whitehorn]

As of r277990, the powerpc64 kernel in 11-CURRENT is now a different 
executable format (PIE). If you update past this revision, you *must* 
make sure that you update loader(8) (through updating world) *before* 
you reboot with a new kernel. If you do not this, your machine will not 
boot (although you should be able to recover by booting kernel.old from 
the loader prompt).
-Nathan