First batch of changes so that we can compile the code on windows
without cygwin. With these changes gmsh compiles and runs cleanly
without solver/jpeg/png/triangle/netgen/gsl support.

- clarify Combine commands
- explain the funcdamental difference between post-pro options and post-pro plugins

note for fltk 1.1.7

with node ordering corresponding to positive orientation (volume).
Test implemented for 1st and 2nd order elements, but only 1st order hexas
have actually been tested!

fix copy/paste: netgen->ann

simpler tetgen integration by Jozef Vesely

generalized the solver interface to allow permanent listening on a
socket for whoever wants to connect (gmsh -listen)

the polling should also be less CPU hungry in this new version

next step is to add new commands to the protocol so that solvers can
directly transmit data to merge (geometry, mesh, etc.) in addition to
messages and filenames

missing cast

fix time step printf format

missing cast

- new option to choose the mesh element labels (element number, elementary
  entity number, physical entity number or partition number)

doc trsf surf orientation option

fix memory leak + missing depend

ex of sphere meshed with hexas

Please don't load solver plugins by default: for the vast majority of users,
the structural solver options don't make any sense.

Just add Solver.Plugins=1 in your option file if you need that stuff.

finer control of time/timestep display