Merge branch 'jc/add-2.0-delete-default' (early part)

Merge branch 'jc/add-2.0-delete-default' (early part)

Preparatory steps to make "git add <pathspec>" take notice of
removed paths that match <pathspec> by default in Git 2.0.

* 'jc/add-2.0-delete-default' (early part):
  git add: rephrase the "removal will cease to be ignored" warning
  git add: rework the logic to warn "git add <pathspec>..." default change
  git add: start preparing for "git add <pathspec>..." to default to "-A"
  builtin/add.c: simplify boolean variables