[trac759] Makefile fix

src/lib/python/isc/config/Makefile.am

 SUBDIRS = . tests
 
-python_PYTHON = __init__.py ccsession.py cfgmgr.py config_data.py module_spec.py cfgmgr_messages.py
+python_PYTHON = __init__.py ccsession.py cfgmgr.py config_data.py module_spec.py
+
+nodist_python_PYTHON = cfgmgr_messages.py
 
 pythondir = $(pyexecdir)/isc/config
 
@@ -14,6 +16,8 @@ CLEANDIRS = __pycache__
 
 EXTRA_DIST = cfgmgr_messages.mes
 
+BUILT_SOURCES = cfgmgr_messages.py
+
 all-local: cfgmgr_messages.py
 
 clean-local: