Log Message:
Updated gsl to 2.3.

* What is new in gsl-2.3:

** bug fix in documentation for gsl_linalg_LU_refine
   (bug #49728, Joey De Pauw)

** added gsl_multifit_linear_tsvd and gsl_multifit_wlinear_tsvd
   to give user more control over cutoff for truncated SVD

** added routines for Generalized Cross Validation for
   regularized linear least squares

** improved rstat example program and added documentation for
   gsl_rstat_sd_mean (Jonathan Leto)

** added function gsl_multifit_linear_rank

** bug fix in nonlinear least squares when using data weights with
   finite-difference Jacobian

** add 2D subspace method for large systems (multilarge_nlinear)

** bug fix in gsl_ran_beta for small parameters
   (bug #47646, Yu Liu)

** bug fix in gsl_complex_tan for negative imaginary arguments
   (bug #47347, Yu Liu)

** doc bug fix: value of golden ratio

** fixed scaling issue in 2D subspace nonlinear least squares
   method

** optimize dogleg methods to calculate Gauss-Newton point
   only when needed