title: Git submodule update gives "error: invalid key (newline)"
body: <p>After a painful merge, when I run <code>git submodule update</code>, I get this:</p>
  
  <pre><code>&gt;git submodule update
  
  error: invalid key (newline): submodule.external/mono-reactive
  external/mono-reactive.url
  error: invalid key (newline): submodule.external/mono-reactive
  external/mono-reactive.update
  </code></pre>
  
  <p>What's the matter?</p>