try_dlopen() has a bug: it sometimes returns a handle if a dependency

	try_dlopen() has a bug: it sometimes returns a handle if a dependency
	library can't be loaded.  It also returns an error status, however
	lt_dlopenext() doesn't handle this well and returns the invalid handle.
	This causes a segfault instead of a graceful exit.  Update ltdl to
	give an error telling the user to report the problem, so that we can
	try to reproduce it and report to the libtool folks.  We could just
	leave ltdl unpatched; FR will exit either way.