Make exiting with message a function of the exception

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/reclass/errors.py b/reclass/errors.py
index bb81e19..66b1839 100644
--- a/reclass/errors.py
+++ b/reclass/errors.py
@@ -7,7 +7,7 @@
 # Released under the terms of the Artistic Licence 2.0
 #
 
-import posix
+import posix, sys
 
 class ReclassException(Exception):
 
@@ -20,6 +20,10 @@
 
     rc = property(lambda self: self._rc)
 
+    def exit_with_message(self, out=sys.stderr):
+        print >>out, self.message
+        sys.exit(self.rc)
+
 
 class InvocationError(ReclassException):