- #inputMode error
  now issues a FatalError on duplicate entries

- #inputMode warn
  issues a warning on duplicate entries, corresponds to the
  old behaviour of 'error'

- #inputMode protect
  prevents overwriting existing entries

The 'protect' mode provides a simple mechanism for supplying default values.
eg,
    in file1:
        #inputMode  protect
        intensity       0.1;
        mixingLength    0.005;
        #inputMode  merge

        inlet
        {
            type        turbulentIntensityKineticEnergyInlet;
            intensity   $intensity;
        }

    which is included from file2:

        intensity   0.05;
        #include    "file1"

- can use 'XX.empty()' instead of 'XX.size() == 0', 'XX.size() < 1' or
  'XX.size() <= 0' or for simpler coding.
  It also has the same number of characters as '!XX.size()' and /might/ be
  more readable

- many size checking had 'XX.size() > 0', 'XX.size() != 0', or 'XX.size() >= 1'
  when a simple 'XX.size()' suffices

  * added '#remove' function
  * changed insert() method name to more general execute()
  * using #inputMode or #remove within a primitiveEntry now provokes an error
  * adjusted the dictionaryTest accordingly