added File->Clear + changed behaviour of File->New (now just adds a
new model)

allow smaller fonts for palettes (test with "-deltafontsize")

use display list for 3d arrows (approx. 2x speedup on my laptop for
large vector views) and spheres

removed static quadrics (wrong when \exists multiple gl contexts),
replaced with correct(?) init in drawContext

- fix bb computation to avoid model jumping around when adding points in z=0 plane
- pass interpol matrices as ref

window with experimental tree browser

There's no new functionality for now: PLEASE TEST THAT EVERYTHING
WORKS AS IT USED TO BEFORE.

- don't die silently when a read function fails
- fixed while bunch of compiler warnings

fixed-size C strings

****************************************************************
**** PLEASE TEST YOUR SCRIPTS (ESPECIALLY ONES WITH LISTS, *****
****        COMPLICATED AFFECTATIONS, ETC.)                *****
****************************************************************

(only if the current model is not empty: if it's empty it probably mean
we just launched gmsh, and we don't want to delete variables set e.g.
using the -string command line option)

all this open/merge stuff needs to be cleaned up

things down when you have many many surfaces)
- fix out of bound acces in transfinite callback when selecting > 100
entities