Pull up following revision(s) (requested by mrg in ticket #785):
sbin/gpt/gpt.c: revision 1.74
sbin/gpt/map.c: revision 1.14
sbin/gpt/gpt.8: revision 1.53
sbin/gpt/gpt.8: revision 1.54
sbin/gpt/gpt.8: revision 1.55
sbin/gpt/gpt.8: revision 1.56
sbin/gpt/gpt.8: revision 1.57
sbin/gpt/gpt.8: revision 1.59

Add note about bootme flag:
        The bootme flag is used to indicate which partiotion should be booted
        by UEFI boot code.

Fix a typo, and make a couple of minor wording improvements.
I resisted the (very weak) impulse to Americanise some spellings ...

Use Fx/Nx.

clarify that alignment is the number of bytes to align to.

Explain what suffixes are accepted when specifying a size.
Spelling

add information about how to boot from gpt.  mostly taken from the wiki.

if a new map entry doesn't fit, be more verbose about the sizes.

(martin)