corrected error that was added by a faulty diff (!)
Bug 1926: Changed "Close all windows" to "Close all but Main Window"
- fix for Bug 1942: use qpointer list to be able to validate window pointers
- fix for bug 1964: export of function definitions used in raterules / assignment rules only.
- fix for bug 1966: now a member variable controls that functions are only exported once.
- bug 1973: always write the metabolite attribute for metaboliteGlyph, even when it is not referenced. that way older versions of COPASI won't refuse to load the model