Add a new variant of dlclose() Valgrind suppressions to fix a Buildbot issue.

mysql-test/valgrind.supp

@@ -414,6 +414,20 @@
    fun:_Z13plugin_dl_delPK19st_mysql_lex_string
 }
 
+{
+   dlclose memory loss from plugin variant 4, seen on Ubuntu Jaunty i686
+   Memcheck:Leak
+   fun:malloc
+   fun:_dl_close_worker
+   fun:_dl_close
+   fun:dlclose_doit
+   fun:_dl_catch_error
+   fun:_dlerror_run
+   fun:dlclose
+   fun:_Z15free_plugin_memP12st_plugin_dl
+   fun:_Z13plugin_dl_delPK19st_mysql_lex_string
+}
+
 {
    dlclose memory loss from plugin variant 4
    Memcheck:Leak