2 small mods for T. Schumacher

trying to fix problem reported by T. Schumacher: use double[16] instead of
double[4][4] for opengl matrices

fix view name

HarmonicToTime

New Plugin(HarmonicToTime)

better detection of the view number

missing #ifdef HAVE_FLTK

New (very simple, but very nice IMHO) callback mechanism in plugins: a
plugin can now set the min/max/step in input fields, and draw
arbitrary stuff when the values are modified.

This makes the plugin interface MUCH nicer: the plane in CutPlane is
defined interactively (a la "Clipping planes"), the sphere in
CutSphere is visible, the min/max values in CutMap reflect the min/max
in the view, etc.

Fixed bug in second order mesh of closed curves

New options to enable/desable all default post-processing/solver plugins

add error check in Oriente()

add point with 'e', too

proof of concept for unproject (e.g. to add points with the mouse)

fix gcc warning + add "cancel" button to make the dialog look like
the other ones

- make the rotation matrix a matrix of doubles (instead of floats)

- store the modelview and the projection matrices in CTX

- new unproject() routine to transform window coordinates to model
  coordinates

- cleaned up all the static variables in the Opengl_Window class

- small fix to reduce normal clamping when zooming

Say we didn't find any solver plugins if GMSHPLUGINSHOME is not defined.

This is not perfect, but it allows us to *not* display the annoying
popups for "regular" users, while still registering JF's solver plugin...

'External data source' -> 'Data source'

if we have no geometry and no mesh, use the max of all view bounding boxes
(instead of the bounding box of the last view only)

typo

small cleanup + better error detection

allow x,y,z in expressions

init mesh fails for very thin regions

forgot to update help strings

The new "External data source" option makes the "Vector type->Raised
view" unnecessary. Just select "Vector type->Displacement" and choose
the data source from any other view in the list--including "Self"!

added small option to color the arrows representing a vector field
according to the data from another view

new option to draw the arrows with a fixed size

added a call to GUI::check() to make the GUI more responsive

add note on tensor field display

2nd order view example from JF

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