Stopping conditon of dual CD method for L1- and L2-loss SVM is changed

Stopping conditon of dual CD method for L1- and L2-loss SVM is changed

Currently the stopping condition is M-m <= \epsilon, where

M = max proj_gard(alpha) and m = min proj_grad(alpha).

This condition works well in practice, but we must ensure that the
following situation does not occur.

  M, m >> 0  or M,m << 0
but
  M - m <= \epsilon.

From the optimality condition, |M| and |m| must be close to zero.
For example, because

  grad_i f(0) = -1, for all i.

M=m= -1 and they satisfy M-m <= \epsilon.  Thus we add |M| <=\epsilon
and |m| <= \epsilon$ into the stopping condition.  In fact we can use
only these two inequalities as the stopping condition, but for
historical reasons we keep M-m <= \epsilon as the main condition to
check.