Currently the GTK L&F has two modes:
  - native mode (GTKNativeEngine, GTKNativeStyle), which is used when the native
    GTK libraries are available and meet our minimum requirements (basically GTK+ 2.2);
    this mode uses native GTK API calls to render widgets
  - default mode (GTKDefaultEngine, GTKDefaultStyle), which is used only as a backup
    when the native GTK libraries are not available or do not meet our requirements;
    this mode uses pure Java rendering code to emulate a very rudimentary theme

Today we only use the default engine in a very small percentage of cases, primarily
on Solaris 9 when the old (beta, never publicly released or supported) GNOME 2.0
desktop is in use, and I suppose we might use it on ridiculously old Linux boxes
that have something less than GTK+ 2.2 installed. Since both of these scenarios
are unsupported, the default engine is nothing more than a maintenance burden.
If we removed GTKDefaultEngine and GTKDefaultStyle and folded GTKNativeEngine and
GTKNativeStyle functionality into their base classes, we could streamline the
GTK L&F by removing about 2000 lines of unneeded code. This will allow us to focus
on improving the design of the GTK L&F without having to worry about making things
work for both default and native modes.