stronger deprecation

[Havoc Pennington <hp redhat com>]

Hi,

An ongoing problem is that people try to use interfaces that simply
_don't work_, such as GtkTree. The widget doesn't work; but there are
a whole lot of posts on gtk-list where people are trying to use
it. And all those people are wasting their time, maybe a lot of time.

In the case where an interface is not only deprecated, but also known
to be broken and we fully intend to ignore any bug reports against it,
I propose that we require the user to define
GTK_ENABLE_BROKEN_INTERFACES in order to get the header, and so by
default attempts to use GtkTree will not compile.

Other suggestions for solution welcome, but I do think we need to keep
people from wasting time writing new code with broken widgets like
GtkTree and GtkText. There are quite a lot of gtk-list posts caused by
this.

Havoc