Increase the number of particles.

To pass the test on the value of the approximated log-likelihood.

This test should not be included in the testsuite (far too slow)

tests/particle/noisy_ar1_nlf_apf.mod

@@ -36,7 +36,7 @@ options_.particle.status = 1; // Required because we intend to use a nonlinear f
            mode_file=noisy,
            datafile=noisy_ar1_data,
            order=1,
-           number_of_particles = 20000000,
+           number_of_particles = 50000000,
            filter_algorithm=apf);