Better interactive point creation (modified patch from schumact@colorado.edu)

- First draft (pretty much untested!) of new "Integrate" plugin to
  * integrate scalar fields over all the elements in a view
  * integrate the circulation of vector fields along line elements
  * integrate the flux of vector fields across surface elements

  Used with Plugin(DisplacementRaise) and Plugin(Evaluate) this
  permits for example to compute the area/volume of deformed
  configurations; and, with Plugin(CutPlane)+Plugin(Skin), the
  perimeter of deformed sections. Another interesting application is
  to use it on a vector field with Plugin(CutPlane), in order to
  compute fluxes across arbitrary cross-sections.

- Added "connectPoints" option to Plugin(CutParametric) so
  that we can feed its output to Plugin(Integrate)

- Added Normals and Tangents options to visualize the orientation of
  elements in post-processing views

- Added "swapOrientation" in Plugin(Transform) to change the
  orientation of the elements (in place) (+ moved the transformation
  routines from the view class into the plugin)

- fixed #defines in some of the plugin header files

- First draft (pretty much untested!) of new "Integrate" plugin to
  * integrate scalar fields over all the elements in a view
  * integrate the circulation of vector fields along line elements
  * integrate the flux of vector fields across surface elements

  Used with Plugin(DisplacementRaise) and Plugin(Evaluate) this
  permits for example to compute the area/volume of deformed
  configurations; and, with Plugin(CutPlane)+Plugin(Skin), the
  perimeter of deformed sections. Another interesting application is
  to use it on a vector field with Plugin(CutPlane), in order to
  compute fluxes across arbitrary cross-sections.

- Added "connectPoints" option to Plugin(CutParametric) so
  that we can feed its output to Plugin(Integrate)

- Added Normals and Tangents options to visualize the orientation of
  elements in post-processing views

- Added "swapOrientation" in Plugin(Transform) to change the
  orientation of the elements (in place) (+ moved the transformation
  routines from the view class into the plugin)

- fixed #defines in some of the plugin header files

fix gcc warning

pretty print

GUI::reset_option_browser() should not show() the whole option window,
just the appropriate group

cleanup (and remove 2 shift/reduce conflicts in parser)

- avoid querying menu/browser->value() when it doesn't make sense
- fixed out-of-sync option panel when removing views

better error messages+choice selection for "external view" stuff

fix broken english

since Tools->Options->Save behaves like a good citizen now (saving only
stuff that has been modified), we can reduce the number of things that
are saved in .gmshrc

allow a 3rd arg to specify an output filename

Trying to fix (for the 100th time) a home directory issue under some
version of Windows. Thanks to <nicolas.haefele@supelec.fr>.

simpler Sprintf

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)