Issue 166069: Fix assumption that mailboxes have either child directories or messages but not both.

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m :	publish + mail comments
M :	edit review message
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J / K :	jump to next file with a comment after / before current file
	Side-by-side diff
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c :	collapse all comments
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N / P :	next / previous comment
<Up> / <Down> :	next / previous line
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d :	mark current comment as done

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o / <Enter> :	open current patch in side-by-side view
i :	open current patch in unified diff view

	Issue List
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<Ctrl> + s or <Ctrl> + Enter :	save comment
<Esc> :	cancel edit