put fltk popup bug fix in a single header file

draw the rotation center

default tensor type should be 1

fltk does not like the KEYUP thing -- reverting to KEYBOARD

- test <hash_map> (commented out for now)
- added "box" mode to clipping planes GUI

couple more when(FL_RELEASE)

better fix: the window can exist and take events even BEFORE it has been
"updated" for the first time

fix crash

more when(FL_RELEASE) on expenive callbacks

for some of the expensive options, set when(FL_RELEASE). We'll see if we
need to add more later

do_callback() on KEYUP

only do_callback() on release

Options in the GUI are now applied instantenuously.

Please let me know if you see anything weird in the GUI.

- better computation of bounds for discrete entities
- added small widget for light position selection
- infrastructure for Fourier models

much better selection of center of rotation (can select ANY entity now to
prescribe rotation center)

better rgb/hsv conversion

merge dates

add comments

I think picking undo is more intuitive when using maxdepth

msh files should be opened in binary mode (on f&*%^ing Windows)

fix include

extended selection buffer to prepare for mesh element picking and the new
mesh editing interface

simplify TeX printing

reimplemented VertexArrays with std::vector (it's a bit faster)

- done rewriting second order algo

- small optimizations here and there to speed up the vertex array creation
  (we should get rid of List_Add & co)