Improvements:

- The task_manager script accepts an optional argument -w/--wait
  that makes it wait for the named task to start.

- New classes DerivFn and NumDerivFn in Functions.FirstDerivatives.

- New optional validator in Functions.LeastSquares.

- PDB output can handle alternate location fields.

- The NumPy header location is obtained from NumPy during installation.

Bug fixes:

- Better error handling in netCDF array write operations.

- DistributedComputing: improved Windows compatibility