Function File: pol = loadpolars (pn)

Load an airfoil polar data in the form of 4 column matrix, specified as

     <angle of attack> <lift coefficient> <moment coefficient> <drag coefficient>

The angles of attack should form an increasing sequence. pn can either be a single name, a cell array of names, or a structure with a "names" field containing a cell array of names, and a "z" field containing spanwise coordinates of polars. In the latter case, pol.z will contain the z values. Duplicate loads are avoided, i.e. a file specified twice will only be loaded once and then copied.