BUG: avoid duplicate ensight surface mesh/geometries (issue #167)

- ensight does supports geometry in a separate file, but for the
  surface writer we claim that this is not true. This allows
  the field writers to control where the mesh/case files land.

  With 'true', the uncollated output would incidentally create
  things like this:

  Previous (w/ fields)        | Now (w/ fields)
  ----------------------------+----------------------
    0.05/surf.case            |
    0.05/surf.mesh            |
    0.05/p/surf.case          |  0.05/p/surf.case
    0.05/p/surf.mesh          |  0.05/p/surf.mesh
    0.05/p/surf.0000.p        |  0.05/p/surf.0000.p

  Previous (w/o fields)       | Now (w/o fields)
  ----------------------------+----------------------
    0.05/surf.case            | 0.05/surf.mesh
    0.05/surf.case            | 0.05/surf.mesh

  Move the separateGeometry() flag to the *.C code, where it is less
  likely to be mistakenly altered.