patch 7.4.1492

Problem:    No command line completion for ":packadd".
Solution:   Implement completion. (Hirohito Higashi)

src/ex_docmd.c

@@ -4198,6 +4198,11 @@ set_one_cmd_context(
 	    xp->xp_pattern = arg;
 	    break;
 
+	case CMD_packadd:
+	    xp->xp_context = EXPAND_PACKADD;
+	    xp->xp_pattern = arg;
+	    break;
+
 #if (defined(HAVE_LOCALE_H) || defined(X_LOCALE)) \
 	&& (defined(FEAT_GETTEXT) || defined(FEAT_MBYTE))
 	case CMD_language:
@@ -5846,6 +5851,7 @@ static struct
     {EXPAND_SYNTIME, "syntime"},
 #endif
     {EXPAND_SETTINGS, "option"},
+    {EXPAND_PACKADD, "packadd"},
     {EXPAND_SHELLCMD, "shellcmd"},
 #if defined(FEAT_SIGNS)
     {EXPAND_SIGN, "sign"},