multidimensional optimization

[Brian Gough]

I'll provide an alternate method setf which accepts precomputed
function values. That will be the simplest way to handle this case.

Also I'll move the function values (flower,fmin,fupper) into the
algorithm-independent state, so they are more accessible (e.g. so that
the value at the minimum does not have to be recomputed).

Fabrice Rossi writes:
 > 
 > Replace  int (*set) (void *state, gsl_function * f, double * minimum,
 > gsl_interval * x) by
 > int (*set) (void *state, gsl_function * f, double * minimum, gsl_interval *
 > x,unsigned char have_f);
 >