MFC Loader Fixes 2017q4p5: r324557,r324558,r324559,r324646,r324647
r324557: Rename exit to efi_exit to avoid clashing with libsa exit
definition
r324558: Define prototype for exit and ensure references
r324559: Move panic back into libsa. It's documented in libstand(3) to
belong there.
r324646: Unify boot1 with loader.
r324647: Move orphaned man pages into new man directory from common.