Merge branch 'mc/cred-helper-ignore-unknown'

Most credential helpers ignored unknown entries in a credential
description, but a few died upon seeing them.  The latter were
taught to ignore them, too

* mc/cred-helper-ignore-unknown:
  osxkeychain: clarify that we ignore unknown lines
  netrc: ignore unknown lines (do not die)
  wincred: ignore unknown lines (do not die)