Tidy up mdoc formatting for "etc.)" at end of line

man(1) has some logic to use two spaces after a full stop, which is
useful for spotting sentence breaks in monospace fonts. However,
this logic is very simple, treating almost all '.' characters as
end-of-sentence markers, unless followed by certain other
characters. For example, '.,' is not end-of-sentence, and neither
is ".) ", but ".)" at the end of a line triggers the sentence-end
detection.

Apply a zero-width space to a few instances of this in share/man,
and also supply a missing full stop for an instance that occurred at
the end of a sentence.

Leave untouched several instances that are at the end of a sentence
or list element.

Reported by: 0mp (ieee80211.9)