testbot/TestAgent: Quote the unknown command to avoid ambiguity.

[Francois Gouget]

---

After I mistyped a command line I ended up with the 'unknown command 
version' error message which was quite puzzling.

 testbot/scripts/TestAgent |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/testbot/scripts/TestAgent b/testbot/scripts/TestAgent
index 521e741..897ca81 100755
--- a/testbot/scripts/TestAgent
+++ b/testbot/scripts/TestAgent
@@ -188,7 +188,7 @@ while (@ARGV)
     }
     else
     {
-        error("unknown command $arg\n");
+        error("unknown command '$arg'\n");
         $Usage = 2;
     }
 }
-- 
1.7.10.4