[Bug-gsl] Wrong algorithm in gsl_rng_r250

[Andreas Schneider]

The documentation claims that gsl_rng_r250 does

  x_n = x_{n-103} ^ x_{n-250},

but actually the implementation does

  x_n = x_{n-147} ^ x_{n-250}.

This error seems to be very common. It must have been introduced long time ago.

I fed some data from both variants into Marsaglia's diehard and found that the 
documented version is better in most tests. Thus the error is probably in the 
implementation and the documentation is right.

Andreas Schneider