- 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