Add parameter checking for beta/4, make_beta/3, make_beta_2/3.
export new predicates to handle the member of the input list are integers:
  make_beta_int/3
  make_beta_int_2/3
  beta_int/4
simplifies the code
export make-beta-2, make-beta+-2. the same as make-beta, make-beta+, but produce smaller n,m.