gsl: updated to 2.5

What is new in gsl-2.5:

** doc bug fix in binomial distribution figure

** added Wishart distribution

** added new module for digital filtering (gsl_filter); current filters include:
    Gaussian filter
    median filter
    recursive median filter
    impulse detection filter

** added new module for moving window statistics (gsl_movstat)

** added statistics functions:
    gsl_stats_median()
    gsl_stats_select()
    gsl_stats_mad()
    gsl_stats_mad0()
    gsl_stats_Sn_from_sorted_data()
    gsl_stats_Qn_from_sorted_data()
    gsl_stats_gastwirth_from_sorted_data()
    gsl_stats_trmean_from_sorted_data()

** added Romberg integration (gsl_integration_romberg)

** bug fix in deprecated functions gsl_multifit_wlinear_svd and
  gsl_multifit_wlinear_usvd

** documention corrected to state that gsl_sf_legendre functions do
  not include Condon-Shortley phase by default

** bug fix in exponential fitting example when using larger number
  of points

** changed internal workspace inside gsl_spmatrix to a union to
  avoid casting

** bug fixes in ode-initval2 for very rare solver crashing cases

** add histogram2d figure to manual (was missing in 2.4)

** bug fix in gsl_spmatrix_add for duplicate input arguments

** add support for negative arguments nu in gsl_sf_bessel_Jnu and
  gsl_sf_bessel_Ynu

** better texinfo documentation for gsl_sf_hyperg functions

** fix vector and matrix fread/fwrite testing on windows systems
  when tmpfile() fails

** fix for rstat/test.c on PPC64

(adam)