Disabled Checkbox for now; more stuff to do first.
Implemented initial window size on the GTK+ backend.
Switched the GTK+ layout control from GtkLayout back to GtkFixed; the size-allocate thing overrides the size-request issue I had earlier that prompted the switch away.
Actually, switch back to GtkLayout, as GtkFixed has the side effect of not allowing truly arbitrary resizes.
Switched from gtk_init() to the version that lets us catch and report any errors it encounters.
Added Checkbox on the GTK+ backend, added a checkbox to the test program, and fixed a small error in the GTK+ widgetbase.parent() that kept the new widget hidden.
Mostly added Checkbox to the Windows backend; it doesn't show up right away and it crashes in WM_NCDESTROY...
Fixed the RemoveWindowSubclass() crash in Windows Checkboxes.
More TODOs.
Moved Window.SetControl() into window.go pending addition of fake resize events.
Added provisions for proper window redraw on Window.SetParent() and implemented them on Mac OS X; still untested.
Implemented the Control parent/unparent redraw provisions on the GTK+ backend.
Oops, forgot to fill in a name in a comment in the previous commit. Fixed.
Implemented Checkbox on Mac OS X. Also untested; will test next.
Fixed compilation errors on Mac OS X. Reparenting works; redrawing, however...