Options/GUI for partitioning software

fixed-size C strings

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

CGNS I/O rewrite - alpha version