Pull up following revision(s) (requested by martin in ticket #797):
sbin/gpt/gpt.8: 1.60-1.63
sbin/gpt/header.c: 1.9
Make the "gpt header" command return EXIT_FAILURE when no GPT is present.
This helps sysinst to tell a GPT labeled disk from others.
Very lazy version of a change proposed by kre.
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Sort sections.
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Bump date for new EXIT STATUS section.
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Spello.  (it is "existence").
ispell also says that we should s/parseable/parsable/ but I'm
not sure about that one, so I left it.
I also left a correct spelling that no-one has bothered to mangle!

(snj)