[IGSMAIL-6674] Error in IGb08.snx covariance matrix

[Paul Rebischung]

Dear colleagues,

An error was discovered in the covariance matrix of IGb08.snx: the
off-diagonal covariance terms of the newly introduced parameters had been
incorrectly computed. A corrected version of IGb08.snx is now posted at:

ftp://igs-rf.ign.fr/pub/IGb08/IGb08.snx
ftp://igs-rf.ensg.eu/pub/IGb08/IGb08.snx

The parameter values and sigmas are unchanged, so that no modification of
the IGb08.ssc file was necessary.

Many thanks to Shailen Desai for uncovering the problem, and apologies for
the inconvenience,

Paul Rebischung