Add tab completion for pager_min_lines to psql.

This was inadvertantly omitted from commit
7655f4cc. Mea culpa.

Backpatched to 9.5 where pager_min_lines was introduced.

src/bin/psql/tab-complete.c

@@ -3019,8 +3019,8 @@ psql_completion(const char *text, int start, int end)
 		static const char *const my_list[] =
 		{"border", "columns", "expanded", "fieldsep", "fieldsep_zero",
 			"footer", "format", "linestyle", "null", "numericlocale",
-			"pager", "recordsep", "recordsep_zero", "tableattr", "title",
-			"tuples_only", "unicode_border_linestyle",
+			"pager", "pager_min_lines", "recordsep", "recordsep_zero",
+			"tableattr", "title", "tuples_only", "unicode_border_linestyle",
 		"unicode_column_linestyle", "unicode_header_linestyle", NULL};
 
 		COMPLETE_WITH_LIST_CS(my_list);