Add missing argv.h includes.

Noticed these as part of #3694: external libevent's don't cause argv.h
to automatically get included.

Refs trac:3694

This commit was SVN r29897.

The following Trac tickets were found above:
  Ticket 3694 --> https://svn.open-mpi.org/trac/ompi/ticket/3694

orte/mca/oob/base/oob_base_stubs.c

@@ -15,6 +15,7 @@
 
 #include "opal/util/output.h"
 #include "opal/mca/db/db.h"
+#include "opal/util/argv.h"
 
 #include "orte/mca/errmgr/errmgr.h"
 #include "orte/mca/state/state.h"

orte/mca/plm/base/plm_base_proxy.c

@@ -27,6 +27,7 @@
 #include "opal/dss/dss.h"
 #include "opal/util/path.h"
 #include "opal/mca/installdirs/installdirs.h"
+#include "opal/util/argv.h"
 
 #include "orte/util/name_fns.h"
 #include "orte/util/show_help.h"