new solver options: SocketCommand and NameCommand (patch by
<C.Stott@surrey.ac.uk>)

set a parameter for the max number of elements per bucket
(default=100, which seems to be a good memory vs. speed trade-off for
meshes up to 1/2 million elements)

- allow more than 2 elements per bucket for ST!
- add missing tensor simplex case

- fixed out of bound access in OctreePost for multi-step views

- added dView option to StreamLines plugin to interpolate an
  arbitrary scalar view on the stream lines

pretty print

pretty print

pretty print

- cleaned up the octree code (renamed some files, added copyright
  notices, indented everything)

- backported JF's doc from the texinfo file into the c++ code (the
  documentation is actually generated automatically by Gmsh with
  "gmsh -doc"!)

- replaced nPoints with nPointsU and nPointsV in CutGrid

- fixed a couple of printfs + removed some unused variables