ENH: improve startup time for foamToEnsight conversion (issue #240).

Old code:
    Found 10990 time steps
    Search for moving mesh ... no moving mesh detected.
    Startup in 329.09 s

Updated:
    Found 10990 time steps
    Search for moving mesh ... no moving mesh detected.
    Startup in 1.6 s

- Cause was checking "polyMesh/points" via an IOobject.
  Short-circuit with a check for a polyMesh/ directory first.

  Limit the check to the master-node as well to further reduce
  load on the file-system.

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ENH: improve per-step conversion times for foamToEnsight.

Old code:
    Converting 11001 time steps
    Time [0] = 0       Wrote in 1.53 s
    Time [1] = 1       Wrote in 1.52 s
    ...
    Time [100] = 100   Elapsed time 205.35 s

Updated:
    Converting 11001 time steps
    Time [0] = 0       Wrote in 1.4 s
    Time [1] = 1       Wrote in 0.07 s
    ...
    Time [100] = 100   Elapsed time 42.4 s

- Speedup by hashing test results from the first conversion step
  instead of checking each time.

  Check data on all nodes to avoid problems with incomplete writes.

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BUG: moving mesh detection failed for foamToEnsightParts

- adjusted to agree with updated foamToEnsight

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Note:

- foamToEnsightParts (serial) still has about twice the throughput of
  foamToEnsight.