Call: [odata opwr]=freq_int_diff_1D(idata,order,dt); 
  * "odata" is the output data
  * "opwr" is the log power spectrum of the output data
  * "idata" is the input data given as a matrix
  * "order" A positive value N results in a differentialtion of order N. A
     negative value N results in an integration of order N. (e.g. for N=1/2 the array is half differentiated. N = -2 results in a double integration)
  * "dt" is the sample interval
  
  The code will extend the input signal with zeroes to the next power of two
  
  For finite-difference calculations; if a e.g. Ricker pulse has to propagte in
  the grid then a half-integrated (order = -0.5) Ricker pulse has to be
  used as source pulse.
 
  Knud Cordua 2010