gsl 0.8 compile error

[Brian Gough]

Toby White writes:
 > So if you want GSL to work properly under OpenBSD at the moment, you have 
 > to use gsl_log1p. A quick patch to configure.in is included below. I'll try
 > and come up with a better test that actually checks the output of log1p.

Thanks. An automatic test would be useful so that it adapts
automatically on future fixed versions.  It should be sufficient to
pick a few bad values of x and compare with the correct results I
would think.