pml/Makefile.am: add missing file to $(headers)

ompi/mca/pml/Makefile.am

@@ -9,7 +9,7 @@
 #                         University of Stuttgart.  All rights reserved.
 # Copyright (c) 2004-2005 The Regents of the University of California.
 #                         All rights reserved.
-# Copyright (c) 2010 Cisco Systems, Inc.  All rights reserved.
+# Copyright (c) 2010-2015 Cisco Systems, Inc.  All rights reserved.
 # $COPYRIGHT$
 # 
 # Additional copyrights may follow
@@ -22,7 +22,7 @@ noinst_LTLIBRARIES = libmca_pml.la
 libmca_pml_la_SOURCES =
 
 # local files
-headers = pml.h
+headers = pml.h pml_constants.h
 libmca_pml_la_SOURCES += $(headers) $(nodist_headers)
 
 # Conditionally install the header files