seg fault on some global objects upon cleanup

[gewang]

general template:

global Object foo;
<<< Machine.refcount(foo) >>>;
// possible crash at this point

global GPlane foo; (crashes; refcount 1)
GPlane foo; (recount 1)
NOTE: has additional refcounting

global GGen foo; (crashes; refcount 1)
GGen foo; (recount 1)
NOTE: has additional refcounting

global FileTexture foo; (crashes; refcount 1)
FileTexture foo; (recount 1)
NOTE: has additional refcounting

global Geometry foo; (crashes; refcount 1)
Geometry foo; (recount 1)
NOTE: has additional refcounting

global UI_Button foo; (refcount 1)
UI_Button foo; (recount 1)

global OscIn foo; (crashes; refcount 1)
OscIn foo; (refcount 2)

global OscOut foo; (refcount 1)
OscOut foo; (refcount 1)

global Event foo; (refcount 1)
Event foo; (refcount 1)

[gewang]

possible cause: global objects are not checking for default ctors (newly added as 1.5.2.0)
possible fix pushed a0d1786
unit test (for OscIn) fe922d9