Quoted values can still have a trailing comment that we need to remove
before calling `add_value`. Otherwise, when trying to strip the quotes
from the value `string_strip_quotes` only looks at the end which
is inside the comment and so it won't find a matching end quote to
strip.
Fixes#626
Previously config lines like
[rule]
script = mail -s "New notif"
were only possible to get written with additional full quotes,
which makes no sense in command line expressions.
