Better error for unknown brew commands

bin/brew

@@ -23,7 +23,7 @@ case ARGV.first
 when '--cache'
   puts HOMEBREW_CACHE
   exit 0
-when '-h', '--help', '--usage', '-?' 
+when '-h', '--help', '--usage', '-?', nil
   puts ARGV.usage
   exit 0
 when '--version'
@@ -221,7 +221,7 @@ begin
     exec "git", "log", ARGV.formulae.first.path, *ARGV.options
 
   else
-    puts ARGV.usage
+    onoe "Unknown command: #{arg}"
   end
 
 rescue FormulaUnspecifiedError