(cherry picked from commit 05e75ec6)

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(cherry picked from commit 159d2fd2)

(cherry picked from commit bea8906d)

(cherry picked from commit d7122abb)

o When servers are empty, show prefer and noselect as disabled.
o Tighten the config write by using the same code idiom as the
  frontend, which is the safer method.
o Untangle noselect and prefer, ntpd.conf will handle it.

(cherry picked from commit 80eba3c2)

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(cherry picked from commit 3759a297)