Line ending policies were changed in the parent, dccebddb3b80. To make
it easier to resolve downstream merge conflicts after line-ending
policies are adjusted this is a separate whitespace-only commit. If you
have merge conflicts as a result, you can simply `git add --renormalize
-u && git merge --continue` or `git add --renormalize -u && git rebase
--continue` - depending on your workflow.
Change formatv() to validate that the number of arguments passed matches
number of replacement fields in the format string, and that the replacement
indices do not contain holes.
To support cases where this cannot be guaranteed, introduce a formatv()
overload that allows disabling validation with a bool flag as its first argument.
