Add an exception for permission errors

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/reclass/errors.py b/reclass/errors.py
index 66b1839..a327f6d 100644
--- a/reclass/errors.py
+++ b/reclass/errors.py
@@ -25,6 +25,12 @@
         sys.exit(self.rc)
 
 
+class PermissionError(ReclassException):
+
+    def __init__(self, msg, rc=posix.EX_NOPERM):
+        super(PermissionError, self).__init__(msg, rc)
+
+
 class InvocationError(ReclassException):
 
     def __init__(self, msg, rc=posix.EX_USAGE):