allow selection of functions to read in for the PLOT3D reader
Improvement for plot3d reader: if you have a function file, offer a list of which variables to actually read into memory much as done for the more common Q file where you can read/store density, momentum, stagnant energy and/or other derived quantities from these variables (velocity, vorticity, pressure, blah, blah, blah).
Variables in the function file (the .f file for the PLOT3D file, not the .xyz file) come into paraview as "Function0", "Function1", etc, just have a check box list to allow one to say only read Function7 and not the other "FunctionXY"s.
Note: the function structure is similar to the Q file structure