Pull up following revision(s) (requested by jnemeth in ticket #908):

usr.bin/calendar/calendars/calendar.birthday: revision 1.27
usr.bin/calendar/calendars/calendar.christian: revision 1.7
usr.bin/calendar/calendars/calendar.usholiday: revision 1.8
usr.bin/calendar/calendars/calendar.netbsd: revision 1.39
usr.bin/calendar/calendars/calendar.holiday: revision 1.28
usr.bin/calendar/calendars/calendar.holiday: revision 1.29
usr.bin/calendar/calendars/calendar.judaic: revision 1.7
usr.bin/calendar/calendars/calendar.history: revision 1.35

Only 35 years late.

Mention the Sand Creek massacre.

Fix a typo.

(or, `Emily Dickinson' - the American poet - was born on the same date)

Update calendar files for the upcoming NetBSD 8.0 release.  I'm
assuming that it will be released by August 1, which is two months
from now.  Thus I used 2018 dates for all holidays between Aug.
1st and Dec. 31st, and 2019 dates for all holidays between Jan.
1st and Jul. 31st.

(martin)