Merge branch 'jc/show-untracked-false'

Merge branch 'jc/show-untracked-false'

The status.showUntrackedFiles configuration variable had a name
that tempts users to set a Boolean value expressed in our usual
"false", "off", and "0", but it only took "no".  This has been
corrected so "true" and its synonyms are taken as "normal", while
"false" and its synonyms are taken as "no".

* jc/show-untracked-false:
  status: allow --untracked=false and friends
  status: unify parsing of --untracked= and status.showUntrackedFiles