Fix the panic message so that it looks more like M5's panic.

Make it so the same path is not added to the system path twice.

--HG--
extra : convert_revision : fe18db38cc4e335ad3525a364e9f8faf62b60e52

sim/pyconfig/m5config.py

@@ -36,11 +36,12 @@ env = {}
 env.update(os.environ)
 
 def panic(*args, **kwargs):
-    sys.exit(*args, **kwargs)
+    print >>sys.stderr, 'panic:', string
+    sys.exit(1)
 
 def AddToPath(path):
     path = os.path.realpath(path)
-    if os.path.isdir(path):
+    if os.path.isdir(path) and path not in sys.path:
         sys.path.append(path)
 
 def Import(path):