more boxed types

[James Henstridge <james daa com au>]

One thing I would like to see before the API freeze is to add get_type()
calls for more of the boxed types in gtk+ (and maybe pango).  The ones I
could think of off the top of my head were:
  GdkCursor
  GdkDevice
  GtkCTreeNode (questionable; deprecated widget, but type needed for LBs)

Having typecodes for these types is helpful if some addon library wants to
use them as signal arguments, and can also be helpful in language bindings
(my python bindings now have code that makes it very easy to handle types
that have been registered as boxed types).

Fixing the first two should be fairly easy, and non intrusive.  The last
would involve registering null handlers for the copy and release functions
for the boxed type, and adjust the argument lists for GtkCTree's signals.

I will put together a patch for this.

James.