Change the tolerance from 1e-2 to 1e-1 in the function 'mpi_fit_pars_errors'

The tolerance not only determines how precisely a confidence limit
is to be determined, see help("conf"), but also gives the tolerance
for chi^2 improvements without interrupting the search for the
confidence intervals, see help("mpi_fit_pars"). For instance, if
confidence limits for delta chi^2 = x are desired, the absolute chi^2
of a new best fit has to be better than 0.5*tolerance*x to call for
a restart, see file isis.git/src/fit-chisqrconf.c.