Processing of all FLTK events as well as window resizing while the file chooser runs is suspended,
Normal event processing and resizing is restored when chooser closes.
Under the X11 platform, class Fl_Native_File_Chooser will behave as follows :
- if the KDE desktop is used and if command "kdialog" is available in the path,
the Qt/KDE file chooser is used;
- otherwise, if the GTK library is available at run-time,
the GTK file chooser is used;
- otherwise, the FLTK file chooser is used.
In addition, when Fl::OPTION_FNFC_USES_GTK is off, the FLTK file chooser
is always used.
