1.2.50 `sm1.generalized_bfunction'
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sm1.generalized_bfunction(I,V,VD,W)
     :   It computes the generalized b-function (indicial equation) of I
      with respect to the weight W.

   Description:

     It no longer calls sm1's original function. Instead, it calls
     asir "generic_bfct".


   Example:
      sm1.generalized_bfunction([x^2*dx^2-1/2,dy^2],[x,y],[dx,dy],[-1,0,1,0]);

