pyapi FEATURE add class to represent and access NETCONF error-reply

The class is connected with exception raised when NETCONF error reply
is received. The object of the new class (holding the error info) is
then connected with the exception which makes it available to the caller.
diff --git a/python/setup.py.in b/python/setup.py.in
index 2a459d3..f537a8f 100644
--- a/python/setup.py.in
+++ b/python/setup.py.in
@@ -5,7 +5,8 @@
                                     "${CMAKE_CURRENT_SOURCE_DIR}/session.c", 
                                     "${CMAKE_CURRENT_SOURCE_DIR}/ssh.c",
                                     "${CMAKE_CURRENT_SOURCE_DIR}/tls.c",
-                                    "${CMAKE_CURRENT_SOURCE_DIR}/rpc.c"
+                                    "${CMAKE_CURRENT_SOURCE_DIR}/rpc.c",
+                                    "${CMAKE_CURRENT_SOURCE_DIR}/err.c"
                                    ],
                            depends=["${CMAKE_CURRENT_SOURCE_DIR}/netconf.h",
                                     "${CMAKE_CURRENT_SOURCE_DIR}/session.h",