compile tetgen by default so we get feedback on machine-specific problems

New plugin to compute the modulus and the phase of a complex-valued field
in-place, in one simple step. One could already do this with Plugin(Evaluate),
but it was a little bit cumbersome.

Removed the last bits of the "Discrete Surface/Line" stuff.

Gmsh can now simply read a .msh file, and use it as the boundary mesh
of a 3D mesh. For an example on how to do this, cf.
demos/sphere-discrete.geo.

This complements nicely the STL remeshing stuff: Gmsh can now
for example very easily be used to extrude surface meshes that
come from other tools.

reorder

fixed full-quadrangle recombine algo:

- run globally, not for each surface
- assign entities to elements
- split line meshes
- correctly re-tag vertices as 1st order
- plug memory leaks

fixed small bug when drawing the boundary of a prism for a time step > 1

replaced ExportLCField with ExportMeshStatistics (lc + gamma, eta, rho + elem num)

optimize 2d iso plots with vertex arrays

2 big optimizations for meshes that contain a lot of line elements:

- speed up Read_Mesh (by introducing temp tree in curves)
- use vertex arrays for lines in mesh drawing code

removed remaining Discrete Line/Surface stuff

add entries about Visibility, Clipping and Transparency

add link to pdf tutorial

typo

link to GUI tutorial

- changed "View.ArrowLocation" into "View.GlyphLocation" (this way we can
  also use this option to display the numeric values at the nodes,
  instead of displaying always at the barycenter)

- changed the numeric display of vectors (display the 3 omponents
  instead of the norm)

added small warning in automatically generated opt_* files

removed limit on number of file names allowed on the command line

better help string for '-combine'

added all the missing "Combine" modes in the parser

doc 2nd order elements

- Generalized the "View" parser so that we can add new elements more easily
  (the code is *much* shorter, but unfortunately about 10-15% slower)

- Upgraded all post-pro file formats to handle curved (second order)
  elements: SL2, VL2, TL2, ST2, VT2, ... The new version number for the
  postpro files is 1.4

- Added code to automatically split the curved elements into linear
  elements when the view is created. WARNING: this is only a temporary
  solution: weshould generalize Adaptive_Post_View to handle these curved
  elements.

typos