Add function ut_array_1d_int_gmean.

ut_array_1d_int_gmean computes the geometric mean of a 1D integer array.
Add ut_array_1d_set_3.

The function 'ut_array_1d_set_3' enables to set the values of a 1D array
of size 3.
Change functions in ut_arg.

Changed ut_arg_nextas* functions to take the pointer of the result as
argument.  This avoids memory leak issues when dealing with character
strings.

ut_arg_nextaschar has been renamed to ut_arg_nextasstring.